mbox series

[v4,0/5] x86: Enable LKGS instruction

Message ID 20221019102310.1543-1-xin3.li@intel.com
Headers
Series x86: Enable LKGS instruction |

Message

Li, Xin3 Oct. 19, 2022, 10:23 a.m. UTC 
  LKGS instruction is introduced with Intel FRED (flexible return and event
delivery) specification https://cdrdv2.intel.com/v1/dl/getContent/678938.

LKGS is independent of FRED, so we enable it as a standalone CPU feature.

LKGS behaves like the MOV to GS instruction except that it loads the base
address into the IA32_KERNEL_GS_BASE MSR instead of the GS segment’s
descriptor cache, which is exactly what Linux kernel does to load user level
GS base.  Thus, with LKGS, there is no need to SWAPGS away from the kernel
GS base.

Changes since v3:
* We want less ASM not more, thus keep local_irq_save/restore() inside
  native_load_gs_index() (Thomas Gleixner).
* For paravirt enabled kernels, initialize pv_ops.cpu.load_gs_index to
  native_lkgs (Thomas Gleixner).

Changes since V2:
* Add "" not to show "lkgs" in /proc/cpuinfo (Chang S. Bae).
* Mark DI as input and output (+D) as in V1, since the exception handler
  modifies it (Brian Gerst).

Changes since V1:
* Use EX_TYPE_ZERO_REG instead of fixup code in the obsolete .fixup code
  section (Peter Zijlstra).
* Add a comment that states the LKGS_DI macro will be repalced with "lkgs %di"
  once the binutils support the LKGS instruction (Peter Zijlstra).

H. Peter Anvin (Intel) (5):
  x86/cpufeature: add the cpu feature bit for LKGS
  x86/opcode: add the LKGS instruction to x86-opcode-map
  x86/gsseg: make asm_load_gs_index() take an u16
  x86/gsseg: move load_gs_index() to its own new header file
  x86/gsseg: use the LKGS instruction if available for load_gs_index()

 arch/x86/entry/entry_64.S                |  2 +-
 arch/x86/ia32/ia32_signal.c              |  1 +
 arch/x86/include/asm/cpufeatures.h       |  1 +
 arch/x86/include/asm/gsseg.h             | 66 ++++++++++++++++++++++++
 arch/x86/include/asm/mmu_context.h       |  1 +
 arch/x86/include/asm/special_insns.h     | 21 --------
 arch/x86/kernel/cpu/common.c             |  1 +
 arch/x86/kernel/paravirt.c               |  1 +
 arch/x86/kernel/tls.c                    |  1 +
 arch/x86/lib/x86-opcode-map.txt          |  1 +
 tools/arch/x86/include/asm/cpufeatures.h |  1 +
 tools/arch/x86/lib/x86-opcode-map.txt    |  1 +
 12 files changed, 76 insertions(+), 22 deletions(-)
 create mode 100644 arch/x86/include/asm/gsseg.h

Comments

Thomas Gleixner Oct. 19, 2022, 2:12 p.m. UTC | #1 
Xin,

On Wed, Oct 19 2022 at 03:23, Xin Li wrote:
> LKGS instruction is introduced with Intel FRED (flexible return and event
> delivery) specification https://cdrdv2.intel.com/v1/dl/getContent/678938.

So I have two versions of the same thing in my inbox now. What's the
difference?
Li, Xin3 Oct. 19, 2022, 5:03 p.m. UTC | #2 
> On Wed, Oct 19 2022 at 03:23, Xin Li wrote:
> > LKGS instruction is introduced with Intel FRED (flexible return and
> > event
> > delivery) specification https://cdrdv2.intel.com/v1/dl/getContent/678938.
> 
> So I have two versions of the same thing in my inbox now. What's the
> difference?

No difference at all.

Sorry for the confusion, but maybe I have an excuse. A few days ago,
I sent an email to the LKML and it seems lost. I got to know it until
Nathan Chancellor replied; and my original message doesn't show up here:
https://lore.kernel.org/all/Y02eZ6A%2Fvlj8+B%2Fc@dev-arch.thelio-3990X/

Last night I sent this patch set to the LKML and waited half an hour,
they still didn't show up, so I did it again, but this time both worked.

I have sent an email to owner-linux-kernel@vger.kernel.org asking for help.

Xin
Li, Xin3 Nov. 18, 2022, 7:25 a.m. UTC | #3 
> > On Wed, Oct 19 2022 at 03:23, Xin Li wrote:
> > > LKGS instruction is introduced with Intel FRED (flexible return and
> > > event
> > > delivery) specification https://cdrdv2.intel.com/v1/dl/getContent/678938.
> >
> > So I have two versions of the same thing in my inbox now. What's the
> > difference?

Hi Thomas,

Should I resend it?

Xin


> 
> No difference at all.
> 
> Sorry for the confusion, but maybe I have an excuse. A few days ago, I sent an
> email to the LKML and it seems lost. I got to know it until Nathan Chancellor
> replied; and my original message doesn't show up here:
> https://lore.kernel.org/all/Y02eZ6A%2Fvlj8+B%2Fc@dev-arch.thelio-3990X/
> 
> Last night I sent this patch set to the LKML and waited half an hour, they still
> didn't show up, so I did it again, but this time both worked.
> 
> I have sent an email to owner-linux-kernel@vger.kernel.org asking for help.
> 
> Xin