[PATCHv11,0/9] mm, x86/cc, efi: Implement support for unaccepted memory

  UEFI Specification version 2.9 introduces the concept of memory
acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
SEV-SNP, requiring memory to be accepted before it can be used by the
guest. Accepting happens via a protocol specific for the Virtual
Machine platform.

Accepting memory is costly and it makes VMM allocate memory for the
accepted guest physical address range. It's better to postpone memory
acceptance until memory is needed. It lowers boot time and reduces
memory overhead.

The kernel needs to know what memory has been accepted. Firmware
communicates this information via memory map: a new memory type --
EFI_UNACCEPTED_MEMORY -- indicates such memory.

Range-based tracking works fine for firmware, but it gets bulky for
the kernel: e820 has to be modified on every page acceptance. It leads
to table fragmentation, but there's a limited number of entries in the
e820 table

Another option is to mark such memory as usable in e820 and track if the
range has been accepted in a bitmap. One bit in the bitmap represents
2MiB in the address space: one 4k page is enough to track 64GiB or
physical address space.

In the worst-case scenario -- a huge hole in the middle of the
address space -- It needs 256MiB to handle 4PiB of the address
space.

Any unaccepted memory that is not aligned to 2M gets accepted upfront.

The approach lowers boot time substantially. Boot to shell is ~2.5x
faster for 4G TDX VM and ~4x faster for 64G.

TDX-specific code isolated from the core of unaccepted memory support. It
supposed to help to plug-in different implementation of unaccepted memory
such as SEV-SNP.

-- Fragmentation study --

Vlastimil and Mel were concern about effect of unaccepted memory on
fragmentation prevention measures in page allocator. I tried to evaluate
it, but it is tricky. As suggested I tried to run multiple parallel kernel
builds and follow how often kmem:mm_page_alloc_extfrag gets hit.

See results in the v9 of the patchset[1][2]

[1] https://lore.kernel.org/all/20230330114956.20342-1-kirill.shutemov@linux.intel.com
[2] https://lore.kernel.org/all/20230416191940.ex7ao43pmrjhru2p@box.shutemov.name

--

The tree can be found here:

https://github.com/intel/tdx.git guest-unaccepted-memory

The patchset depends on MAX_ORDER changes in MM tree.

v11:
 - Restructure the code to make it less x86-specific (suggested by Ard):
   + use EFI configuration table instead of zero-page to pass down bitmap;
   + do not imply 1bit == 2M in bitmap;
   + move bulk of the code under driver/firmware/efi;
 - The bitmap only covers unaccpeted memory now. All memory that is not covered
   by the bitmap assumed accepted;
 - Reviewed-by from Ard;
v10:
 - Restructure code around zones_with_unaccepted_pages static brach to avoid
   unnecessary function calls (Suggested by Vlastimil);
 - Drop mentions of PageUnaccepted();
 - Drop patches that add fake unaccepted memory support and sysfs handle to
   accept memory manually;
 - Add Reviewed-by from Vlastimil;
v9:
 - Accept memory up to high watermark when kernel runs out of free memory;
 - Treat unaccepted memory as unusable in __zone_watermark_unusable_free();
 - Per-zone unaccepted memory accounting;
 - All pages on unaccepted list are MAX_ORDER now;
 - accept_memory=eager in cmdline to pre-accept memory during the boot;
 - Implement fake unaccepted memory;
 - Sysfs handle to accept memory manually;
 - Drop PageUnaccepted();
 - Rename unaccepted_pages static key to zones_with_unaccepted_pages;
v8:
 - Rewrite core-mm support for unaccepted memory (patch 02/14);
 - s/UnacceptedPages/Unaccepted/ in meminfo;
 - Drop arch/x86/boot/compressed/compiler.h;
 - Fix build errors;
 - Adjust commit messages and comments;
 - Reviewed-bys from Dave and Borislav;
 - Rebased to tip/master.
v7:
 - Rework meminfo counter to use PageUnaccepted() and move to generic code;
 - Fix range_contains_unaccepted_memory() on machines without unaccepted memory;
 - Add Reviewed-by from David;
v6:
 - Fix load_unaligned_zeropad() on machine with unaccepted memory;
 - Clear PageUnaccepted() on merged pages, leaving it only on head;
 - Clarify error handling in allocate_e820();
 - Fix build with CONFIG_UNACCEPTED_MEMORY=y, but without TDX;
 - Disable kexec at boottime instead of build conflict;
 - Rebased to tip/master;
 - Spelling fixes;
 - Add Reviewed-by from Mike and David;
v5:
 - Updates comments and commit messages;
   + Explain options for unaccepted memory handling;
 - Expose amount of unaccepted memory in /proc/meminfo
 - Adjust check in page_expected_state();
 - Fix error code handling in allocate_e820();
 - Centralize __pa()/__va() definitions in the boot stub;
 - Avoid includes from the main kernel in the boot stub;
 - Use an existing hole in boot_param for unaccepted_memory, instead of adding
   to the end of the structure;
 - Extract allocate_unaccepted_memory() form allocate_e820();
 - Complain if there's unaccepted memory, but kernel does not support it;
 - Fix vmstat counter;
 - Split up few preparatory patches;
 - Random readability adjustments;
v4:
 - PageBuddyUnaccepted() -> PageUnaccepted;
 - Use separate page_type, not shared with offline;
 - Rework interface between core-mm and arch code;
 - Adjust commit messages;
 - Ack from Mike;

Kirill A. Shutemov (9):
  mm: Add support for unaccepted memory
  efi/x86: Get full memory map in allocate_e820()
  efi/libstub: Implement support for unaccepted memory
  x86/boot/compressed: Handle unaccepted memory
  efi: Provide helpers for unaccepted memory
  efi/unaccepted: Avoid load_unaligned_zeropad() stepping into
    unaccepted memory
  x86/tdx: Make _tdx_hypercall() and __tdx_module_call() available in
    boot stub
  x86/tdx: Refactor try_accept_one()
  x86/tdx: Add unaccepted memory support

 arch/x86/Kconfig                              |   2 +
 arch/x86/boot/compressed/Makefile             |   1 +
 arch/x86/boot/compressed/efi.h                |   1 +
 arch/x86/boot/compressed/error.c              |  19 ++
 arch/x86/boot/compressed/error.h              |   1 +
 arch/x86/boot/compressed/kaslr.c              |  35 ++-
 arch/x86/boot/compressed/mem.c                |  42 ++++
 arch/x86/boot/compressed/misc.c               |   6 +
 arch/x86/boot/compressed/misc.h               |   6 +
 arch/x86/boot/compressed/tdx-shared.c         |   2 +
 arch/x86/boot/compressed/tdx.c                |  37 +++
 arch/x86/coco/tdx/Makefile                    |   2 +-
 arch/x86/coco/tdx/tdx-shared.c                |  95 ++++++++
 arch/x86/coco/tdx/tdx.c                       | 118 +---------
 arch/x86/include/asm/efi.h                    |   2 +
 arch/x86/include/asm/shared/tdx.h             |  53 +++++
 arch/x86/include/asm/tdx.h                    |  21 +-
 arch/x86/include/asm/unaccepted_memory.h      |  23 ++
 drivers/base/node.c                           |   7 +
 drivers/firmware/efi/Kconfig                  |  14 ++
 drivers/firmware/efi/Makefile                 |   1 +
 drivers/firmware/efi/efi.c                    |   7 +
 drivers/firmware/efi/libstub/Makefile         |   2 +
 drivers/firmware/efi/libstub/bitmap.c         |  41 ++++
 drivers/firmware/efi/libstub/efistub.h        |   6 +
 drivers/firmware/efi/libstub/find.c           |  43 ++++
 .../firmware/efi/libstub/unaccepted_memory.c  | 222 ++++++++++++++++++
 drivers/firmware/efi/libstub/x86-stub.c       |  39 +--
 drivers/firmware/efi/unaccepted_memory.c      | 138 +++++++++++
 fs/proc/meminfo.c                             |   5 +
 include/linux/efi.h                           |  13 +-
 include/linux/mm.h                            |  19 ++
 include/linux/mmzone.h                        |   8 +
 mm/internal.h                                 |   1 +
 mm/memblock.c                                 |   9 +
 mm/mm_init.c                                  |   7 +
 mm/page_alloc.c                               | 173 ++++++++++++++
 mm/vmstat.c                                   |   3 +
 38 files changed, 1060 insertions(+), 164 deletions(-)
 create mode 100644 arch/x86/boot/compressed/mem.c
 create mode 100644 arch/x86/boot/compressed/tdx-shared.c
 create mode 100644 arch/x86/coco/tdx/tdx-shared.c
 create mode 100644 arch/x86/include/asm/unaccepted_memory.h
 create mode 100644 drivers/firmware/efi/libstub/bitmap.c
 create mode 100644 drivers/firmware/efi/libstub/find.c
 create mode 100644 drivers/firmware/efi/libstub/unaccepted_memory.c
 create mode 100644 drivers/firmware/efi/unaccepted_memory.c
  

On 5/13/23 17:04, Kirill A. Shutemov wrote:
> UEFI Specification version 2.9 introduces the concept of memory
> acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
> SEV-SNP, requiring memory to be accepted before it can be used by the
> guest. Accepting happens via a protocol specific for the Virtual
> Machine platform.
> 
> Accepting memory is costly and it makes VMM allocate memory for the
> accepted guest physical address range. It's better to postpone memory
> acceptance until memory is needed. It lowers boot time and reduces
> memory overhead.
> 
> The kernel needs to know what memory has been accepted. Firmware
> communicates this information via memory map: a new memory type --
> EFI_UNACCEPTED_MEMORY -- indicates such memory.
> 
> Range-based tracking works fine for firmware, but it gets bulky for
> the kernel: e820 has to be modified on every page acceptance. It leads
> to table fragmentation, but there's a limited number of entries in the
> e820 table
> 
> Another option is to mark such memory as usable in e820 and track if the
> range has been accepted in a bitmap. One bit in the bitmap represents
> 2MiB in the address space: one 4k page is enough to track 64GiB or
> physical address space.
> 
> In the worst-case scenario -- a huge hole in the middle of the
> address space -- It needs 256MiB to handle 4PiB of the address
> space.
> 
> Any unaccepted memory that is not aligned to 2M gets accepted upfront.
> 
> The approach lowers boot time substantially. Boot to shell is ~2.5x
> faster for 4G TDX VM and ~4x faster for 64G.
> 
> TDX-specific code isolated from the core of unaccepted memory support. It
> supposed to help to plug-in different implementation of unaccepted memory
> such as SEV-SNP.
> 
> -- Fragmentation study --
> 
> Vlastimil and Mel were concern about effect of unaccepted memory on
> fragmentation prevention measures in page allocator. I tried to evaluate
> it, but it is tricky. As suggested I tried to run multiple parallel kernel
> builds and follow how often kmem:mm_page_alloc_extfrag gets hit.
> 
> See results in the v9 of the patchset[1][2]
> 
> [1] https://lore.kernel.org/all/20230330114956.20342-1-kirill.shutemov@linux.intel.com
> [2] https://lore.kernel.org/all/20230416191940.ex7ao43pmrjhru2p@box.shutemov.name
> 
> --
> 
> The tree can be found here:
> 
> https://github.com/intel/tdx.git guest-unaccepted-memory

I get some failures when building without TDX support selected in my
kernel config after adding unaccepted memory support for SNP:

   In file included from arch/x86/boot/compressed/../../coco/tdx/tdx-shared.c:1,
                    from arch/x86/boot/compressed/tdx-shared.c:2:
   ./arch/x86/include/asm/tdx.h: In function ‘tdx_kvm_hypercall’:
   ./arch/x86/include/asm/tdx.h:72:17: error: ‘ENODEV’ undeclared (first use in this function)
      72 |         return -ENODEV;
         |                 ^~~~~~
   ./arch/x86/include/asm/tdx.h:72:17: note: each undeclared identifier is reported only once for each function it appears in

Adding an include for linux/errno.h gets past that error, but then
I get the following:

   ld: arch/x86/boot/compressed/tdx-shared.o: in function `tdx_enc_status_changed_phys':
   tdx-shared.c:(.text+0x42): undefined reference to `__tdx_hypercall'
   ld: tdx-shared.c:(.text+0x7f): undefined reference to `__tdx_module_call'
   ld: tdx-shared.c:(.text+0xce): undefined reference to `__tdx_module_call'
   ld: tdx-shared.c:(.text+0x13b): undefined reference to `__tdx_module_call'
   ld: tdx-shared.c:(.text+0x153): undefined reference to `cc_mkdec'
   ld: tdx-shared.c:(.text+0x15d): undefined reference to `cc_mkdec'
   ld: tdx-shared.c:(.text+0x18e): undefined reference to `__tdx_hypercall'
   ld: arch/x86/boot/compressed/vmlinux: hidden symbol `__tdx_hypercall' isn't defined
   ld: final link failed: bad value

So it looks like arch/x86/boot/compressed/tdx-shared.c is being
built, while arch/x86/boot/compressed/tdx.c isn't.

After setting TDX in the kernel config, I can build successfully, but
I'm running into an error when trying to accept memory during
decompression.

In drivers/firmware/efi/libstub/unaccepted_memory.c, I can see that the
unaccepted_table is allocated, but when accept_memory() is invoked the
table address is now zero. I thought maybe it had to do with bss, but even
putting it in the .data section didn't help. I'll keep digging, but if you
have any ideas, that would be great.

Thanks,
Tom

> 
> The patchset depends on MAX_ORDER changes in MM tree.
> 
> v11:
>   - Restructure the code to make it less x86-specific (suggested by Ard):
>     + use EFI configuration table instead of zero-page to pass down bitmap;
>     + do not imply 1bit == 2M in bitmap;
>     + move bulk of the code under driver/firmware/efi;
>   - The bitmap only covers unaccpeted memory now. All memory that is not covered
>     by the bitmap assumed accepted;
>   - Reviewed-by from Ard;
> v10:
>   - Restructure code around zones_with_unaccepted_pages static brach to avoid
>     unnecessary function calls (Suggested by Vlastimil);
>   - Drop mentions of PageUnaccepted();
>   - Drop patches that add fake unaccepted memory support and sysfs handle to
>     accept memory manually;
>   - Add Reviewed-by from Vlastimil;
> v9:
>   - Accept memory up to high watermark when kernel runs out of free memory;
>   - Treat unaccepted memory as unusable in __zone_watermark_unusable_free();
>   - Per-zone unaccepted memory accounting;
>   - All pages on unaccepted list are MAX_ORDER now;
>   - accept_memory=eager in cmdline to pre-accept memory during the boot;
>   - Implement fake unaccepted memory;
>   - Sysfs handle to accept memory manually;
>   - Drop PageUnaccepted();
>   - Rename unaccepted_pages static key to zones_with_unaccepted_pages;
> v8:
>   - Rewrite core-mm support for unaccepted memory (patch 02/14);
>   - s/UnacceptedPages/Unaccepted/ in meminfo;
>   - Drop arch/x86/boot/compressed/compiler.h;
>   - Fix build errors;
>   - Adjust commit messages and comments;
>   - Reviewed-bys from Dave and Borislav;
>   - Rebased to tip/master.
> v7:
>   - Rework meminfo counter to use PageUnaccepted() and move to generic code;
>   - Fix range_contains_unaccepted_memory() on machines without unaccepted memory;
>   - Add Reviewed-by from David;
> v6:
>   - Fix load_unaligned_zeropad() on machine with unaccepted memory;
>   - Clear PageUnaccepted() on merged pages, leaving it only on head;
>   - Clarify error handling in allocate_e820();
>   - Fix build with CONFIG_UNACCEPTED_MEMORY=y, but without TDX;
>   - Disable kexec at boottime instead of build conflict;
>   - Rebased to tip/master;
>   - Spelling fixes;
>   - Add Reviewed-by from Mike and David;
> v5:
>   - Updates comments and commit messages;
>     + Explain options for unaccepted memory handling;
>   - Expose amount of unaccepted memory in /proc/meminfo
>   - Adjust check in page_expected_state();
>   - Fix error code handling in allocate_e820();
>   - Centralize __pa()/__va() definitions in the boot stub;
>   - Avoid includes from the main kernel in the boot stub;
>   - Use an existing hole in boot_param for unaccepted_memory, instead of adding
>     to the end of the structure;
>   - Extract allocate_unaccepted_memory() form allocate_e820();
>   - Complain if there's unaccepted memory, but kernel does not support it;
>   - Fix vmstat counter;
>   - Split up few preparatory patches;
>   - Random readability adjustments;
> v4:
>   - PageBuddyUnaccepted() -> PageUnaccepted;
>   - Use separate page_type, not shared with offline;
>   - Rework interface between core-mm and arch code;
>   - Adjust commit messages;
>   - Ack from Mike;
> 
> Kirill A. Shutemov (9):
>    mm: Add support for unaccepted memory
>    efi/x86: Get full memory map in allocate_e820()
>    efi/libstub: Implement support for unaccepted memory
>    x86/boot/compressed: Handle unaccepted memory
>    efi: Provide helpers for unaccepted memory
>    efi/unaccepted: Avoid load_unaligned_zeropad() stepping into
>      unaccepted memory
>    x86/tdx: Make _tdx_hypercall() and __tdx_module_call() available in
>      boot stub
>    x86/tdx: Refactor try_accept_one()
>    x86/tdx: Add unaccepted memory support
> 
>   arch/x86/Kconfig                              |   2 +
>   arch/x86/boot/compressed/Makefile             |   1 +
>   arch/x86/boot/compressed/efi.h                |   1 +
>   arch/x86/boot/compressed/error.c              |  19 ++
>   arch/x86/boot/compressed/error.h              |   1 +
>   arch/x86/boot/compressed/kaslr.c              |  35 ++-
>   arch/x86/boot/compressed/mem.c                |  42 ++++
>   arch/x86/boot/compressed/misc.c               |   6 +
>   arch/x86/boot/compressed/misc.h               |   6 +
>   arch/x86/boot/compressed/tdx-shared.c         |   2 +
>   arch/x86/boot/compressed/tdx.c                |  37 +++
>   arch/x86/coco/tdx/Makefile                    |   2 +-
>   arch/x86/coco/tdx/tdx-shared.c                |  95 ++++++++
>   arch/x86/coco/tdx/tdx.c                       | 118 +---------
>   arch/x86/include/asm/efi.h                    |   2 +
>   arch/x86/include/asm/shared/tdx.h             |  53 +++++
>   arch/x86/include/asm/tdx.h                    |  21 +-
>   arch/x86/include/asm/unaccepted_memory.h      |  23 ++
>   drivers/base/node.c                           |   7 +
>   drivers/firmware/efi/Kconfig                  |  14 ++
>   drivers/firmware/efi/Makefile                 |   1 +
>   drivers/firmware/efi/efi.c                    |   7 +
>   drivers/firmware/efi/libstub/Makefile         |   2 +
>   drivers/firmware/efi/libstub/bitmap.c         |  41 ++++
>   drivers/firmware/efi/libstub/efistub.h        |   6 +
>   drivers/firmware/efi/libstub/find.c           |  43 ++++
>   .../firmware/efi/libstub/unaccepted_memory.c  | 222 ++++++++++++++++++
>   drivers/firmware/efi/libstub/x86-stub.c       |  39 +--
>   drivers/firmware/efi/unaccepted_memory.c      | 138 +++++++++++
>   fs/proc/meminfo.c                             |   5 +
>   include/linux/efi.h                           |  13 +-
>   include/linux/mm.h                            |  19 ++
>   include/linux/mmzone.h                        |   8 +
>   mm/internal.h                                 |   1 +
>   mm/memblock.c                                 |   9 +
>   mm/mm_init.c                                  |   7 +
>   mm/page_alloc.c                               | 173 ++++++++++++++
>   mm/vmstat.c                                   |   3 +
>   38 files changed, 1060 insertions(+), 164 deletions(-)
>   create mode 100644 arch/x86/boot/compressed/mem.c
>   create mode 100644 arch/x86/boot/compressed/tdx-shared.c
>   create mode 100644 arch/x86/coco/tdx/tdx-shared.c
>   create mode 100644 arch/x86/include/asm/unaccepted_memory.h
>   create mode 100644 drivers/firmware/efi/libstub/bitmap.c
>   create mode 100644 drivers/firmware/efi/libstub/find.c
>   create mode 100644 drivers/firmware/efi/libstub/unaccepted_memory.c
>   create mode 100644 drivers/firmware/efi/unaccepted_memory.c
>
  

On Tue, May 16, 2023 at 05:41:55PM -0500, Tom Lendacky wrote:
> On 5/13/23 17:04, Kirill A. Shutemov wrote:
> > UEFI Specification version 2.9 introduces the concept of memory
> > acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
> > SEV-SNP, requiring memory to be accepted before it can be used by the
> > guest. Accepting happens via a protocol specific for the Virtual
> > Machine platform.
> > 
> > Accepting memory is costly and it makes VMM allocate memory for the
> > accepted guest physical address range. It's better to postpone memory
> > acceptance until memory is needed. It lowers boot time and reduces
> > memory overhead.
> > 
> > The kernel needs to know what memory has been accepted. Firmware
> > communicates this information via memory map: a new memory type --
> > EFI_UNACCEPTED_MEMORY -- indicates such memory.
> > 
> > Range-based tracking works fine for firmware, but it gets bulky for
> > the kernel: e820 has to be modified on every page acceptance. It leads
> > to table fragmentation, but there's a limited number of entries in the
> > e820 table
> > 
> > Another option is to mark such memory as usable in e820 and track if the
> > range has been accepted in a bitmap. One bit in the bitmap represents
> > 2MiB in the address space: one 4k page is enough to track 64GiB or
> > physical address space.
> > 
> > In the worst-case scenario -- a huge hole in the middle of the
> > address space -- It needs 256MiB to handle 4PiB of the address
> > space.
> > 
> > Any unaccepted memory that is not aligned to 2M gets accepted upfront.
> > 
> > The approach lowers boot time substantially. Boot to shell is ~2.5x
> > faster for 4G TDX VM and ~4x faster for 64G.
> > 
> > TDX-specific code isolated from the core of unaccepted memory support. It
> > supposed to help to plug-in different implementation of unaccepted memory
> > such as SEV-SNP.
> > 
> > -- Fragmentation study --
> > 
> > Vlastimil and Mel were concern about effect of unaccepted memory on
> > fragmentation prevention measures in page allocator. I tried to evaluate
> > it, but it is tricky. As suggested I tried to run multiple parallel kernel
> > builds and follow how often kmem:mm_page_alloc_extfrag gets hit.
> > 
> > See results in the v9 of the patchset[1][2]
> > 
> > [1] https://lore.kernel.org/all/20230330114956.20342-1-kirill.shutemov@linux.intel.com
> > [2] https://lore.kernel.org/all/20230416191940.ex7ao43pmrjhru2p@box.shutemov.name
> > 
> > --
> > 
> > The tree can be found here:
> > 
> > https://github.com/intel/tdx.git guest-unaccepted-memory
> 
> I get some failures when building without TDX support selected in my
> kernel config after adding unaccepted memory support for SNP:
> 
>   In file included from arch/x86/boot/compressed/../../coco/tdx/tdx-shared.c:1,
>                    from arch/x86/boot/compressed/tdx-shared.c:2:
>   ./arch/x86/include/asm/tdx.h: In function ‘tdx_kvm_hypercall’:
>   ./arch/x86/include/asm/tdx.h:72:17: error: ‘ENODEV’ undeclared (first use in this function)
>      72 |         return -ENODEV;
>         |                 ^~~~~~
>   ./arch/x86/include/asm/tdx.h:72:17: note: each undeclared identifier is reported only once for each function it appears in
> 
> Adding an include for linux/errno.h gets past that error, but then
> I get the following:
> 
>   ld: arch/x86/boot/compressed/tdx-shared.o: in function `tdx_enc_status_changed_phys':
>   tdx-shared.c:(.text+0x42): undefined reference to `__tdx_hypercall'
>   ld: tdx-shared.c:(.text+0x7f): undefined reference to `__tdx_module_call'
>   ld: tdx-shared.c:(.text+0xce): undefined reference to `__tdx_module_call'
>   ld: tdx-shared.c:(.text+0x13b): undefined reference to `__tdx_module_call'
>   ld: tdx-shared.c:(.text+0x153): undefined reference to `cc_mkdec'
>   ld: tdx-shared.c:(.text+0x15d): undefined reference to `cc_mkdec'
>   ld: tdx-shared.c:(.text+0x18e): undefined reference to `__tdx_hypercall'
>   ld: arch/x86/boot/compressed/vmlinux: hidden symbol `__tdx_hypercall' isn't defined
>   ld: final link failed: bad value
> 
> So it looks like arch/x86/boot/compressed/tdx-shared.c is being
> built, while arch/x86/boot/compressed/tdx.c isn't.

Right. I think this should help:

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 78f67e0a2666..b13a58021086 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -106,8 +106,8 @@ ifdef CONFIG_X86_64
 endif

 vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
-vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
-vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o $(obj)/tdx-shared.o
+vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o $(obj)/tdx-shared.o
+vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o

 vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
 vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o

> After setting TDX in the kernel config, I can build successfully, but
> I'm running into an error when trying to accept memory during
> decompression.
> 
> In drivers/firmware/efi/libstub/unaccepted_memory.c, I can see that the
> unaccepted_table is allocated, but when accept_memory() is invoked the
> table address is now zero. I thought maybe it had to do with bss, but even
> putting it in the .data section didn't help. I'll keep digging, but if you
> have any ideas, that would be great.

Not right away. But maybe seeing your side of enabling would help.
  

On 5/16/23 18:22, Kirill A. Shutemov wrote:
> On Tue, May 16, 2023 at 05:41:55PM -0500, Tom Lendacky wrote:
>> On 5/13/23 17:04, Kirill A. Shutemov wrote:
>>> UEFI Specification version 2.9 introduces the concept of memory
>>> acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
>>> SEV-SNP, requiring memory to be accepted before it can be used by the
>>> guest. Accepting happens via a protocol specific for the Virtual
>>> Machine platform.
>>>
>>> Accepting memory is costly and it makes VMM allocate memory for the
>>> accepted guest physical address range. It's better to postpone memory
>>> acceptance until memory is needed. It lowers boot time and reduces
>>> memory overhead.
>>>
>>> The kernel needs to know what memory has been accepted. Firmware
>>> communicates this information via memory map: a new memory type --
>>> EFI_UNACCEPTED_MEMORY -- indicates such memory.
>>>
>>> Range-based tracking works fine for firmware, but it gets bulky for
>>> the kernel: e820 has to be modified on every page acceptance. It leads
>>> to table fragmentation, but there's a limited number of entries in the
>>> e820 table
>>>
>>> Another option is to mark such memory as usable in e820 and track if the
>>> range has been accepted in a bitmap. One bit in the bitmap represents
>>> 2MiB in the address space: one 4k page is enough to track 64GiB or
>>> physical address space.
>>>
>>> In the worst-case scenario -- a huge hole in the middle of the
>>> address space -- It needs 256MiB to handle 4PiB of the address
>>> space.
>>>
>>> Any unaccepted memory that is not aligned to 2M gets accepted upfront.
>>>
>>> The approach lowers boot time substantially. Boot to shell is ~2.5x
>>> faster for 4G TDX VM and ~4x faster for 64G.
>>>
>>> TDX-specific code isolated from the core of unaccepted memory support. It
>>> supposed to help to plug-in different implementation of unaccepted memory
>>> such as SEV-SNP.
>>>
>>> -- Fragmentation study --
>>>
>>> Vlastimil and Mel were concern about effect of unaccepted memory on
>>> fragmentation prevention measures in page allocator. I tried to evaluate
>>> it, but it is tricky. As suggested I tried to run multiple parallel kernel
>>> builds and follow how often kmem:mm_page_alloc_extfrag gets hit.
>>>
>>> See results in the v9 of the patchset[1][2]
>>>
>>> [1] https://lore.kernel.org/all/20230330114956.20342-1-kirill.shutemov@linux.intel.com
>>> [2] https://lore.kernel.org/all/20230416191940.ex7ao43pmrjhru2p@box.shutemov.name
>>>
>>> --
>>>
>>> The tree can be found here:
>>>
>>> https://github.com/intel/tdx.git guest-unaccepted-memory
>>
>> I get some failures when building without TDX support selected in my
>> kernel config after adding unaccepted memory support for SNP:
>>
>>    In file included from arch/x86/boot/compressed/../../coco/tdx/tdx-shared.c:1,
>>                     from arch/x86/boot/compressed/tdx-shared.c:2:
>>    ./arch/x86/include/asm/tdx.h: In function ?tdx_kvm_hypercall?:
>>    ./arch/x86/include/asm/tdx.h:72:17: error: ?ENODEV? undeclared (first use in this function)
>>       72 |         return -ENODEV;
>>          |                 ^~~~~~
>>    ./arch/x86/include/asm/tdx.h:72:17: note: each undeclared identifier is reported only once for each function it appears in
>>
>> Adding an include for linux/errno.h gets past that error, but then
>> I get the following:
>>
>>    ld: arch/x86/boot/compressed/tdx-shared.o: in function `tdx_enc_status_changed_phys':
>>    tdx-shared.c:(.text+0x42): undefined reference to `__tdx_hypercall'
>>    ld: tdx-shared.c:(.text+0x7f): undefined reference to `__tdx_module_call'
>>    ld: tdx-shared.c:(.text+0xce): undefined reference to `__tdx_module_call'
>>    ld: tdx-shared.c:(.text+0x13b): undefined reference to `__tdx_module_call'
>>    ld: tdx-shared.c:(.text+0x153): undefined reference to `cc_mkdec'
>>    ld: tdx-shared.c:(.text+0x15d): undefined reference to `cc_mkdec'
>>    ld: tdx-shared.c:(.text+0x18e): undefined reference to `__tdx_hypercall'
>>    ld: arch/x86/boot/compressed/vmlinux: hidden symbol `__tdx_hypercall' isn't defined
>>    ld: final link failed: bad value
>>
>> So it looks like arch/x86/boot/compressed/tdx-shared.c is being
>> built, while arch/x86/boot/compressed/tdx.c isn't.
> 
> Right. I think this should help:
> 
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 78f67e0a2666..b13a58021086 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -106,8 +106,8 @@ ifdef CONFIG_X86_64
>   endif
> 
>   vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
> -vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
> -vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o $(obj)/tdx-shared.o
> +vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o $(obj)/tdx-shared.o
> +vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
> 
>   vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
>   vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
> 
>> After setting TDX in the kernel config, I can build successfully, but
>> I'm running into an error when trying to accept memory during
>> decompression.
>>
>> In drivers/firmware/efi/libstub/unaccepted_memory.c, I can see that the
>> unaccepted_table is allocated, but when accept_memory() is invoked the
>> table address is now zero. I thought maybe it had to do with bss, but even
>> putting it in the .data section didn't help. I'll keep digging, but if you
>> have any ideas, that would be great.
> 
> Not right away. But maybe seeing your side of enabling would help.

Let me get something pushed up where you can access it and I'll also send
you my kernel config.

In the mean time I added the following and everything worked. But I'm not
sure how acceptable it is to always be checking for the table when the
value is zero is.


diff --git a/drivers/firmware/efi/libstub/unaccepted_memory.c b/drivers/firmware/efi/libstub/unaccepted_memory.c
index f4642c4f25dd..8c5632ab1208 100644
--- a/drivers/firmware/efi/libstub/unaccepted_memory.c
+++ b/drivers/firmware/efi/libstub/unaccepted_memory.c
@@ -183,8 +183,13 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
  	unsigned long bitmap_size;
  	u64 unit_size;
  
-	if (!unaccepted_table)
-		return;
+	if (!unaccepted_table) {
+		efi_guid_t unaccepted_table_guid = LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID;
+
+		unaccepted_table = get_efi_config_table(unaccepted_table_guid);
+		if (!unaccepted_table)
+			return;
+	}
  
  	unit_size = unaccepted_table->unit_size;
  

Thanks,
Tom

>
  

On Wed, May 17, 2023 at 09:32:27AM -0500, Tom Lendacky wrote:
> On 5/16/23 18:22, Kirill A. Shutemov wrote:
> > On Tue, May 16, 2023 at 05:41:55PM -0500, Tom Lendacky wrote:
> > > On 5/13/23 17:04, Kirill A. Shutemov wrote:
> > > > UEFI Specification version 2.9 introduces the concept of memory
> > > > acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
> > > > SEV-SNP, requiring memory to be accepted before it can be used by the
> > > > guest. Accepting happens via a protocol specific for the Virtual
> > > > Machine platform.
> > > > 
> > > > Accepting memory is costly and it makes VMM allocate memory for the
> > > > accepted guest physical address range. It's better to postpone memory
> > > > acceptance until memory is needed. It lowers boot time and reduces
> > > > memory overhead.
> > > > 
> > > > The kernel needs to know what memory has been accepted. Firmware
> > > > communicates this information via memory map: a new memory type --
> > > > EFI_UNACCEPTED_MEMORY -- indicates such memory.
> > > > 
> > > > Range-based tracking works fine for firmware, but it gets bulky for
> > > > the kernel: e820 has to be modified on every page acceptance. It leads
> > > > to table fragmentation, but there's a limited number of entries in the
> > > > e820 table
> > > > 
> > > > Another option is to mark such memory as usable in e820 and track if the
> > > > range has been accepted in a bitmap. One bit in the bitmap represents
> > > > 2MiB in the address space: one 4k page is enough to track 64GiB or
> > > > physical address space.
> > > > 
> > > > In the worst-case scenario -- a huge hole in the middle of the
> > > > address space -- It needs 256MiB to handle 4PiB of the address
> > > > space.
> > > > 
> > > > Any unaccepted memory that is not aligned to 2M gets accepted upfront.
> > > > 
> > > > The approach lowers boot time substantially. Boot to shell is ~2.5x
> > > > faster for 4G TDX VM and ~4x faster for 64G.
> > > > 
> > > > TDX-specific code isolated from the core of unaccepted memory support. It
> > > > supposed to help to plug-in different implementation of unaccepted memory
> > > > such as SEV-SNP.
> > > > 
> > > > -- Fragmentation study --
> > > > 
> > > > Vlastimil and Mel were concern about effect of unaccepted memory on
> > > > fragmentation prevention measures in page allocator. I tried to evaluate
> > > > it, but it is tricky. As suggested I tried to run multiple parallel kernel
> > > > builds and follow how often kmem:mm_page_alloc_extfrag gets hit.
> > > > 
> > > > See results in the v9 of the patchset[1][2]
> > > > 
> > > > [1] https://lore.kernel.org/all/20230330114956.20342-1-kirill.shutemov@linux.intel.com
> > > > [2] https://lore.kernel.org/all/20230416191940.ex7ao43pmrjhru2p@box.shutemov.name
> > > > 
> > > > --
> > > > 
> > > > The tree can be found here:
> > > > 
> > > > https://github.com/intel/tdx.git guest-unaccepted-memory
> > > 
> > > I get some failures when building without TDX support selected in my
> > > kernel config after adding unaccepted memory support for SNP:
> > > 
> > >    In file included from arch/x86/boot/compressed/../../coco/tdx/tdx-shared.c:1,
> > >                     from arch/x86/boot/compressed/tdx-shared.c:2:
> > >    ./arch/x86/include/asm/tdx.h: In function ?tdx_kvm_hypercall?:
> > >    ./arch/x86/include/asm/tdx.h:72:17: error: ?ENODEV? undeclared (first use in this function)
> > >       72 |         return -ENODEV;
> > >          |                 ^~~~~~
> > >    ./arch/x86/include/asm/tdx.h:72:17: note: each undeclared identifier is reported only once for each function it appears in
> > > 
> > > Adding an include for linux/errno.h gets past that error, but then
> > > I get the following:
> > > 
> > >    ld: arch/x86/boot/compressed/tdx-shared.o: in function `tdx_enc_status_changed_phys':
> > >    tdx-shared.c:(.text+0x42): undefined reference to `__tdx_hypercall'
> > >    ld: tdx-shared.c:(.text+0x7f): undefined reference to `__tdx_module_call'
> > >    ld: tdx-shared.c:(.text+0xce): undefined reference to `__tdx_module_call'
> > >    ld: tdx-shared.c:(.text+0x13b): undefined reference to `__tdx_module_call'
> > >    ld: tdx-shared.c:(.text+0x153): undefined reference to `cc_mkdec'
> > >    ld: tdx-shared.c:(.text+0x15d): undefined reference to `cc_mkdec'
> > >    ld: tdx-shared.c:(.text+0x18e): undefined reference to `__tdx_hypercall'
> > >    ld: arch/x86/boot/compressed/vmlinux: hidden symbol `__tdx_hypercall' isn't defined
> > >    ld: final link failed: bad value
> > > 
> > > So it looks like arch/x86/boot/compressed/tdx-shared.c is being
> > > built, while arch/x86/boot/compressed/tdx.c isn't.
> > 
> > Right. I think this should help:
> > 
> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > index 78f67e0a2666..b13a58021086 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -106,8 +106,8 @@ ifdef CONFIG_X86_64
> >   endif
> > 
> >   vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
> > -vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
> > -vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o $(obj)/tdx-shared.o
> > +vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o $(obj)/tdx-shared.o
> > +vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
> > 
> >   vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
> >   vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
> > 
> > > After setting TDX in the kernel config, I can build successfully, but
> > > I'm running into an error when trying to accept memory during
> > > decompression.
> > > 
> > > In drivers/firmware/efi/libstub/unaccepted_memory.c, I can see that the
> > > unaccepted_table is allocated, but when accept_memory() is invoked the
> > > table address is now zero. I thought maybe it had to do with bss, but even
> > > putting it in the .data section didn't help. I'll keep digging, but if you
> > > have any ideas, that would be great.
> > 
> > Not right away. But maybe seeing your side of enabling would help.
> 
> Let me get something pushed up where you can access it and I'll also send
> you my kernel config.
> 
> In the mean time I added the following and everything worked. But I'm not
> sure how acceptable it is to always be checking for the table when the
> value is zero is.
> 
> 
> diff --git a/drivers/firmware/efi/libstub/unaccepted_memory.c b/drivers/firmware/efi/libstub/unaccepted_memory.c
> index f4642c4f25dd..8c5632ab1208 100644
> --- a/drivers/firmware/efi/libstub/unaccepted_memory.c
> +++ b/drivers/firmware/efi/libstub/unaccepted_memory.c
> @@ -183,8 +183,13 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
>  	unsigned long bitmap_size;
>  	u64 unit_size;
> -	if (!unaccepted_table)
> -		return;
> +	if (!unaccepted_table) {
> +		efi_guid_t unaccepted_table_guid = LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID;
> +
> +		unaccepted_table = get_efi_config_table(unaccepted_table_guid);
> +		if (!unaccepted_table)
> +			return;
> +	}
>  	unit_size = unaccepted_table->unit_size;
> 

Kudos to Ard: if efi_relocate_kernel() triggered, it copies the kernel
image to the new place before the variable gets initialized, so it has to
be initialized explicitly by decompressor.

It also covers the cases when bootloader doesn't use EFI stub, including
kexec cases.

I think this fixup should work.

diff --git a/arch/x86/boot/compressed/efi.h b/arch/x86/boot/compressed/efi.h
index cf475243b6d5..866c0af8b5b9 100644
--- a/arch/x86/boot/compressed/efi.h
+++ b/arch/x86/boot/compressed/efi.h
@@ -16,6 +16,7 @@ typedef guid_t efi_guid_t __aligned(__alignof__(u32));
 #define ACPI_TABLE_GUID				EFI_GUID(0xeb9d2d30, 0x2d88, 0x11d3,  0x9a, 0x16, 0x00, 0x90, 0x27, 0x3f, 0xc1, 0x4d)
 #define ACPI_20_TABLE_GUID			EFI_GUID(0x8868e871, 0xe4f1, 0x11d3,  0xbc, 0x22, 0x00, 0x80, 0xc7, 0x3c, 0x88, 0x81)
 #define EFI_CC_BLOB_GUID			EFI_GUID(0x067b1f5f, 0xcf26, 0x44c5, 0x85, 0x54, 0x93, 0xd7, 0x77, 0x91, 0x2d, 0x42)
+#define LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID	EFI_GUID(0xd5d1de3c, 0x105c, 0x44f9,  0x9e, 0xa9, 0xbc, 0xef, 0x98, 0x12, 0x00, 0x31)
 
 #define EFI32_LOADER_SIGNATURE	"EL32"
 #define EFI64_LOADER_SIGNATURE	"EL64"
@@ -105,6 +106,14 @@ struct efi_setup_data {
 	u64 reserved[8];
 };
 
+struct efi_unaccepted_memory {
+	u32 version;
+	u32 unit_size;
+	u64 phys_base;
+	u64 size;
+	unsigned long bitmap[];
+};
+
 static inline int efi_guidcmp (efi_guid_t left, efi_guid_t right)
 {
 	return memcmp(&left, &right, sizeof (efi_guid_t));
diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
index a4308d077885..0108c97399a5 100644
--- a/arch/x86/boot/compressed/mem.c
+++ b/arch/x86/boot/compressed/mem.c
@@ -1,8 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
-#include "../cpuflags.h"
-#include "../string.h"
 #include "error.h"
+#include "misc.h"
 #include "tdx.h"
 #include <asm/shared/tdx.h>
 
@@ -40,3 +39,25 @@ void arch_accept_memory(phys_addr_t start, phys_addr_t end)
 	else
 		error("Cannot accept memory: unknown platform\n");
 }
+
+void init_unaccepted_memory(void)
+{
+	guid_t guid =  LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID;
+	struct efi_unaccepted_memory *unaccepted_table;
+	unsigned long cfg_table_pa;
+	unsigned int cfg_table_len;
+	int ret;
+
+	ret = efi_get_conf_table(boot_params, &cfg_table_pa, &cfg_table_len);
+	if (ret)
+		error("EFI config table not found.");
+
+	unaccepted_table = (void *)efi_find_vendor_table(boot_params,
+							 cfg_table_pa,
+							 cfg_table_len,
+							 guid);
+	if (unaccepted_table->version != 1)
+		error("Unknown version of unaccepted memory table\n");
+
+	set_unaccepted_table(unaccepted_table);
+}
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index eb8df0d4ad51..36535a3753f5 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -458,6 +458,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 
 	if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY)) {
 		debug_putstr("Accepting memory... ");
+		init_unaccepted_memory();
 		accept_memory(__pa(output), __pa(output) + needed_size);
 	}
 
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 9663d1839f54..e1a0b49e0ed2 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -247,10 +247,10 @@ static inline unsigned long efi_find_vendor_table(struct boot_params *bp,
 }
 #endif /* CONFIG_EFI */
 
-#ifdef CONFIG_UNACCEPTED_MEMORY
+void init_unaccepted_memory(void);
+
+/* Implemented in EFI stub */
+void set_unaccepted_table(struct efi_unaccepted_memory *table);
 void accept_memory(phys_addr_t start, phys_addr_t end);
-#else
-static inline void accept_memory(phys_addr_t start, phys_addr_t end) {}
-#endif
 
 #endif /* BOOT_COMPRESSED_MISC_H */
diff --git a/drivers/firmware/efi/libstub/unaccepted_memory.c b/drivers/firmware/efi/libstub/unaccepted_memory.c
index f4642c4f25dd..fd6a3195c68f 100644
--- a/drivers/firmware/efi/libstub/unaccepted_memory.c
+++ b/drivers/firmware/efi/libstub/unaccepted_memory.c
@@ -6,6 +6,18 @@
 
 static struct efi_unaccepted_memory *unaccepted_table;
 
+/*
+ * Decompressor needs to initialize the variable to cover cases when the table
+ * is not allocated by EFI stub or EFI stub copied the kernel image with
+ * efi_relocate_kernel() before the variable is set.
+ *
+ * It must be call before the first usage of accept_memory() by decompressor.
+ */
+void set_unaccepted_table(struct efi_unaccepted_memory *table)
+{
+	unaccepted_table = table;
+}
+
 efi_status_t allocate_unaccepted_bitmap(__u32 nr_desc,
 					struct efi_boot_memmap *map)
 {
  

On 5/17/23 13:36, Kirill A. Shutemov wrote:
> On Wed, May 17, 2023 at 09:32:27AM -0500, Tom Lendacky wrote:
>> On 5/16/23 18:22, Kirill A. Shutemov wrote:
>>> On Tue, May 16, 2023 at 05:41:55PM -0500, Tom Lendacky wrote:
>>>> On 5/13/23 17:04, Kirill A. Shutemov wrote:
>>>>> UEFI Specification version 2.9 introduces the concept of memory
>>>>> acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
>>>>> SEV-SNP, requiring memory to be accepted before it can be used by the
>>>>> guest. Accepting happens via a protocol specific for the Virtual
>>>>> Machine platform.
>>>>>
>>>>> Accepting memory is costly and it makes VMM allocate memory for the
>>>>> accepted guest physical address range. It's better to postpone memory
>>>>> acceptance until memory is needed. It lowers boot time and reduces
>>>>> memory overhead.
>>>>>
>>>>> The kernel needs to know what memory has been accepted. Firmware
>>>>> communicates this information via memory map: a new memory type --
>>>>> EFI_UNACCEPTED_MEMORY -- indicates such memory.
>>>>>
>>>>> Range-based tracking works fine for firmware, but it gets bulky for
>>>>> the kernel: e820 has to be modified on every page acceptance. It leads
>>>>> to table fragmentation, but there's a limited number of entries in the
>>>>> e820 table
>>>>>
>>>>> Another option is to mark such memory as usable in e820 and track if the
>>>>> range has been accepted in a bitmap. One bit in the bitmap represents
>>>>> 2MiB in the address space: one 4k page is enough to track 64GiB or
>>>>> physical address space.
>>>>>
>>>>> In the worst-case scenario -- a huge hole in the middle of the
>>>>> address space -- It needs 256MiB to handle 4PiB of the address
>>>>> space.
>>>>>
>>>>> Any unaccepted memory that is not aligned to 2M gets accepted upfront.
>>>>>
>>>>> The approach lowers boot time substantially. Boot to shell is ~2.5x
>>>>> faster for 4G TDX VM and ~4x faster for 64G.
>>>>>
>>>>> TDX-specific code isolated from the core of unaccepted memory support. It
>>>>> supposed to help to plug-in different implementation of unaccepted memory
>>>>> such as SEV-SNP.
>>>>>
>>>>> -- Fragmentation study --
>>>>>
>>>>> Vlastimil and Mel were concern about effect of unaccepted memory on
>>>>> fragmentation prevention measures in page allocator. I tried to evaluate
>>>>> it, but it is tricky. As suggested I tried to run multiple parallel kernel
>>>>> builds and follow how often kmem:mm_page_alloc_extfrag gets hit.
>>>>>
>>>>> See results in the v9 of the patchset[1][2]
>>>>>
>>>>> [1] https://lore.kernel.org/all/20230330114956.20342-1-kirill.shutemov@linux.intel.com
>>>>> [2] https://lore.kernel.org/all/20230416191940.ex7ao43pmrjhru2p@box.shutemov.name
>>>>>
>>>>> --
>>>>>
>>>>> The tree can be found here:
>>>>>
>>>>> https://github.com/intel/tdx.git guest-unaccepted-memory
>>>>
>>>> I get some failures when building without TDX support selected in my
>>>> kernel config after adding unaccepted memory support for SNP:
>>>>
>>>>     In file included from arch/x86/boot/compressed/../../coco/tdx/tdx-shared.c:1,
>>>>                      from arch/x86/boot/compressed/tdx-shared.c:2:
>>>>     ./arch/x86/include/asm/tdx.h: In function ?tdx_kvm_hypercall?:
>>>>     ./arch/x86/include/asm/tdx.h:72:17: error: ?ENODEV? undeclared (first use in this function)
>>>>        72 |         return -ENODEV;
>>>>           |                 ^~~~~~
>>>>     ./arch/x86/include/asm/tdx.h:72:17: note: each undeclared identifier is reported only once for each function it appears in
>>>>
>>>> Adding an include for linux/errno.h gets past that error, but then
>>>> I get the following:
>>>>
>>>>     ld: arch/x86/boot/compressed/tdx-shared.o: in function `tdx_enc_status_changed_phys':
>>>>     tdx-shared.c:(.text+0x42): undefined reference to `__tdx_hypercall'
>>>>     ld: tdx-shared.c:(.text+0x7f): undefined reference to `__tdx_module_call'
>>>>     ld: tdx-shared.c:(.text+0xce): undefined reference to `__tdx_module_call'
>>>>     ld: tdx-shared.c:(.text+0x13b): undefined reference to `__tdx_module_call'
>>>>     ld: tdx-shared.c:(.text+0x153): undefined reference to `cc_mkdec'
>>>>     ld: tdx-shared.c:(.text+0x15d): undefined reference to `cc_mkdec'
>>>>     ld: tdx-shared.c:(.text+0x18e): undefined reference to `__tdx_hypercall'
>>>>     ld: arch/x86/boot/compressed/vmlinux: hidden symbol `__tdx_hypercall' isn't defined
>>>>     ld: final link failed: bad value
>>>>
>>>> So it looks like arch/x86/boot/compressed/tdx-shared.c is being
>>>> built, while arch/x86/boot/compressed/tdx.c isn't.
>>>
>>> Right. I think this should help:
>>>
>>> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>>> index 78f67e0a2666..b13a58021086 100644
>>> --- a/arch/x86/boot/compressed/Makefile
>>> +++ b/arch/x86/boot/compressed/Makefile
>>> @@ -106,8 +106,8 @@ ifdef CONFIG_X86_64
>>>    endif
>>>
>>>    vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
>>> -vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
>>> -vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o $(obj)/tdx-shared.o
>>> +vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o $(obj)/tdx-shared.o
>>> +vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
>>>
>>>    vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
>>>    vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
>>>
>>>> After setting TDX in the kernel config, I can build successfully, but
>>>> I'm running into an error when trying to accept memory during
>>>> decompression.
>>>>
>>>> In drivers/firmware/efi/libstub/unaccepted_memory.c, I can see that the
>>>> unaccepted_table is allocated, but when accept_memory() is invoked the
>>>> table address is now zero. I thought maybe it had to do with bss, but even
>>>> putting it in the .data section didn't help. I'll keep digging, but if you
>>>> have any ideas, that would be great.
>>>
>>> Not right away. But maybe seeing your side of enabling would help.
>>
>> Let me get something pushed up where you can access it and I'll also send
>> you my kernel config.
>>
>> In the mean time I added the following and everything worked. But I'm not
>> sure how acceptable it is to always be checking for the table when the
>> value is zero is.
>>
>>
>> diff --git a/drivers/firmware/efi/libstub/unaccepted_memory.c b/drivers/firmware/efi/libstub/unaccepted_memory.c
>> index f4642c4f25dd..8c5632ab1208 100644
>> --- a/drivers/firmware/efi/libstub/unaccepted_memory.c
>> +++ b/drivers/firmware/efi/libstub/unaccepted_memory.c
>> @@ -183,8 +183,13 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
>>   	unsigned long bitmap_size;
>>   	u64 unit_size;
>> -	if (!unaccepted_table)
>> -		return;
>> +	if (!unaccepted_table) {
>> +		efi_guid_t unaccepted_table_guid = LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID;
>> +
>> +		unaccepted_table = get_efi_config_table(unaccepted_table_guid);
>> +		if (!unaccepted_table)
>> +			return;
>> +	}
>>   	unit_size = unaccepted_table->unit_size;
>>
> 
> Kudos to Ard: if efi_relocate_kernel() triggered, it copies the kernel
> image to the new place before the variable gets initialized, so it has to
> be initialized explicitly by decompressor.
> 
> It also covers the cases when bootloader doesn't use EFI stub, including
> kexec cases.
> 
> I think this fixup should work.

Yes, this fixup takes care of the problem I was seeing.

Thanks!
Tom

> 
> diff --git a/arch/x86/boot/compressed/efi.h b/arch/x86/boot/compressed/efi.h
> index cf475243b6d5..866c0af8b5b9 100644
> --- a/arch/x86/boot/compressed/efi.h
> +++ b/arch/x86/boot/compressed/efi.h
> @@ -16,6 +16,7 @@ typedef guid_t efi_guid_t __aligned(__alignof__(u32));
>   #define ACPI_TABLE_GUID				EFI_GUID(0xeb9d2d30, 0x2d88, 0x11d3,  0x9a, 0x16, 0x00, 0x90, 0x27, 0x3f, 0xc1, 0x4d)
>   #define ACPI_20_TABLE_GUID			EFI_GUID(0x8868e871, 0xe4f1, 0x11d3,  0xbc, 0x22, 0x00, 0x80, 0xc7, 0x3c, 0x88, 0x81)
>   #define EFI_CC_BLOB_GUID			EFI_GUID(0x067b1f5f, 0xcf26, 0x44c5, 0x85, 0x54, 0x93, 0xd7, 0x77, 0x91, 0x2d, 0x42)
> +#define LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID	EFI_GUID(0xd5d1de3c, 0x105c, 0x44f9,  0x9e, 0xa9, 0xbc, 0xef, 0x98, 0x12, 0x00, 0x31)
>   
>   #define EFI32_LOADER_SIGNATURE	"EL32"
>   #define EFI64_LOADER_SIGNATURE	"EL64"
> @@ -105,6 +106,14 @@ struct efi_setup_data {
>   	u64 reserved[8];
>   };
>   
> +struct efi_unaccepted_memory {
> +	u32 version;
> +	u32 unit_size;
> +	u64 phys_base;
> +	u64 size;
> +	unsigned long bitmap[];
> +};
> +
>   static inline int efi_guidcmp (efi_guid_t left, efi_guid_t right)
>   {
>   	return memcmp(&left, &right, sizeof (efi_guid_t));
> diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
> index a4308d077885..0108c97399a5 100644
> --- a/arch/x86/boot/compressed/mem.c
> +++ b/arch/x86/boot/compressed/mem.c
> @@ -1,8 +1,7 @@
>   // SPDX-License-Identifier: GPL-2.0-only
>   
> -#include "../cpuflags.h"
> -#include "../string.h"
>   #include "error.h"
> +#include "misc.h"
>   #include "tdx.h"
>   #include <asm/shared/tdx.h>
>   
> @@ -40,3 +39,25 @@ void arch_accept_memory(phys_addr_t start, phys_addr_t end)
>   	else
>   		error("Cannot accept memory: unknown platform\n");
>   }
> +
> +void init_unaccepted_memory(void)
> +{
> +	guid_t guid =  LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID;
> +	struct efi_unaccepted_memory *unaccepted_table;
> +	unsigned long cfg_table_pa;
> +	unsigned int cfg_table_len;
> +	int ret;
> +
> +	ret = efi_get_conf_table(boot_params, &cfg_table_pa, &cfg_table_len);
> +	if (ret)
> +		error("EFI config table not found.");
> +
> +	unaccepted_table = (void *)efi_find_vendor_table(boot_params,
> +							 cfg_table_pa,
> +							 cfg_table_len,
> +							 guid);
> +	if (unaccepted_table->version != 1)
> +		error("Unknown version of unaccepted memory table\n");
> +
> +	set_unaccepted_table(unaccepted_table);
> +}
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index eb8df0d4ad51..36535a3753f5 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -458,6 +458,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
>   
>   	if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY)) {
>   		debug_putstr("Accepting memory... ");
> +		init_unaccepted_memory();
>   		accept_memory(__pa(output), __pa(output) + needed_size);
>   	}
>   
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index 9663d1839f54..e1a0b49e0ed2 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -247,10 +247,10 @@ static inline unsigned long efi_find_vendor_table(struct boot_params *bp,
>   }
>   #endif /* CONFIG_EFI */
>   
> -#ifdef CONFIG_UNACCEPTED_MEMORY
> +void init_unaccepted_memory(void);
> +
> +/* Implemented in EFI stub */
> +void set_unaccepted_table(struct efi_unaccepted_memory *table);
>   void accept_memory(phys_addr_t start, phys_addr_t end);
> -#else
> -static inline void accept_memory(phys_addr_t start, phys_addr_t end) {}
> -#endif
>   
>   #endif /* BOOT_COMPRESSED_MISC_H */
> diff --git a/drivers/firmware/efi/libstub/unaccepted_memory.c b/drivers/firmware/efi/libstub/unaccepted_memory.c
> index f4642c4f25dd..fd6a3195c68f 100644
> --- a/drivers/firmware/efi/libstub/unaccepted_memory.c
> +++ b/drivers/firmware/efi/libstub/unaccepted_memory.c
> @@ -6,6 +6,18 @@
>   
>   static struct efi_unaccepted_memory *unaccepted_table;
>   
> +/*
> + * Decompressor needs to initialize the variable to cover cases when the table
> + * is not allocated by EFI stub or EFI stub copied the kernel image with
> + * efi_relocate_kernel() before the variable is set.
> + *
> + * It must be call before the first usage of accept_memory() by decompressor.
> + */
> +void set_unaccepted_table(struct efi_unaccepted_memory *table)
> +{
> +	unaccepted_table = table;
> +}
> +
>   efi_status_t allocate_unaccepted_bitmap(__u32 nr_desc,
>   					struct efi_boot_memmap *map)
>   {