[RFC,v2,7/8] Introduce dcache_is_aliasing() across all architectures
Commit Message
Introduce a generic way to query whether the dcache is virtually aliased
on all architectures. Its purpose is to ensure that subsystems which
are incompatible with virtually aliased data caches (e.g. FS_DAX) can
reliably query this.
For dcache aliasing, there are three scenarios dependending on the
architecture. Here is a breakdown based on my understanding:
A) The dcache is always aliasing:
* arc
* csky
* m68k (note: shared memory mappings are incoherent ? SHMLBA is missing there.)
* sh
* parisc
B) The dcache aliasing is statically known or depends on querying CPU
state at runtime:
* arm (cache_is_vivt() || cache_is_vipt_aliasing())
* mips (cpu_has_dc_aliases)
* nios2 (NIOS2_DCACHE_SIZE > PAGE_SIZE)
* sparc32 (vac_cache_size > PAGE_SIZE)
* sparc64 (L1DCACHE_SIZE > PAGE_SIZE)
* xtensa (DCACHE_WAY_SIZE > PAGE_SIZE)
C) The dcache is never aliasing:
* alpha
* arm64 (aarch64)
* hexagon
* loongarch (but with incoherent write buffers, which are disabled since
commit d23b7795 ("LoongArch: Change SHMLBA from SZ_64K to PAGE_SIZE"))
* microblaze
* openrisc
* powerpc
* riscv
* s390
* um
* x86
Require architectures in A) and B) to select ARCH_HAS_CACHE_ALIASING and
implement "dcache_is_aliasing()".
Architectures in C) don't select ARCH_HAS_CACHE_ALIASING, and thus
dcache_is_aliasing() simply evaluates to "false".
Note that this leaves "icache_is_aliasing()" to be implemented as future
work. This would be useful to gate features like XIP on architectures
which have aliasing dcache-icache but not dcache-dcache.
Link: https://lore.kernel.org/lkml/20030910210416.GA24258@mail.jlokier.co.uk/
Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-arch@vger.kernel.org
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-cxl@vger.kernel.org
Cc: nvdimm@lists.linux.dev
Cc: linux-xfs@vger.kernel.org
---
arch/arc/Kconfig | 1 +
arch/arc/include/asm/cachetype.h | 9 +++++++++
arch/arm/Kconfig | 1 +
arch/arm/include/asm/cachetype.h | 2 ++
arch/csky/Kconfig | 1 +
arch/csky/include/asm/cachetype.h | 9 +++++++++
arch/m68k/Kconfig | 1 +
arch/m68k/include/asm/cachetype.h | 9 +++++++++
arch/mips/Kconfig | 1 +
arch/mips/include/asm/cachetype.h | 9 +++++++++
arch/nios2/Kconfig | 1 +
arch/nios2/include/asm/cachetype.h | 10 ++++++++++
arch/parisc/Kconfig | 1 +
arch/parisc/include/asm/cachetype.h | 9 +++++++++
arch/sh/Kconfig | 1 +
arch/sh/include/asm/cachetype.h | 9 +++++++++
arch/sparc/Kconfig | 1 +
arch/sparc/include/asm/cachetype.h | 14 ++++++++++++++
arch/xtensa/Kconfig | 1 +
arch/xtensa/include/asm/cachetype.h | 10 ++++++++++
include/linux/cacheinfo.h | 6 ++++++
mm/Kconfig | 6 ++++++
22 files changed, 112 insertions(+)
create mode 100644 arch/arc/include/asm/cachetype.h
create mode 100644 arch/csky/include/asm/cachetype.h
create mode 100644 arch/m68k/include/asm/cachetype.h
create mode 100644 arch/mips/include/asm/cachetype.h
create mode 100644 arch/nios2/include/asm/cachetype.h
create mode 100644 arch/parisc/include/asm/cachetype.h
create mode 100644 arch/sh/include/asm/cachetype.h
create mode 100644 arch/sparc/include/asm/cachetype.h
create mode 100644 arch/xtensa/include/asm/cachetype.h
Comments
On Tue, Jan 30, 2024 at 11:52:54AM -0500, Mathieu Desnoyers wrote:
> Introduce a generic way to query whether the dcache is virtually aliased
> on all architectures. Its purpose is to ensure that subsystems which
> are incompatible with virtually aliased data caches (e.g. FS_DAX) can
> reliably query this.
>
> For dcache aliasing, there are three scenarios dependending on the
> architecture. Here is a breakdown based on my understanding:
>
> A) The dcache is always aliasing:
>
> * arc
> * csky
> * m68k (note: shared memory mappings are incoherent ? SHMLBA is missing there.)
> * sh
> * parisc
/me wonders why the dentry cache aliasing has problems on these
systems.
Oh, dcache != fs/dcache.c (the VFS dentry cache).
Can you please rename this function appropriately so us dumb
filesystem people don't confuse cpu data cache configurations with
the VFS dentry cache aliasing when we read this code? Something like
cpu_dcache_is_aliased(), perhaps?
-Dave.
On 2024-01-30 21:48, Dave Chinner wrote:
> On Tue, Jan 30, 2024 at 11:52:54AM -0500, Mathieu Desnoyers wrote:
>> Introduce a generic way to query whether the dcache is virtually aliased
>> on all architectures. Its purpose is to ensure that subsystems which
>> are incompatible with virtually aliased data caches (e.g. FS_DAX) can
>> reliably query this.
>>
>> For dcache aliasing, there are three scenarios dependending on the
>> architecture. Here is a breakdown based on my understanding:
>>
>> A) The dcache is always aliasing:
>>
>> * arc
>> * csky
>> * m68k (note: shared memory mappings are incoherent ? SHMLBA is missing there.)
>> * sh
>> * parisc
>
> /me wonders why the dentry cache aliasing has problems on these
> systems.
>
> Oh, dcache != fs/dcache.c (the VFS dentry cache).
>
> Can you please rename this function appropriately so us dumb
> filesystem people don't confuse cpu data cache configurations with
> the VFS dentry cache aliasing when we read this code? Something like
> cpu_dcache_is_aliased(), perhaps?
Good point, will do. I'm planning go rename as follows for v3 to
eliminate confusion with dentry cache (and with "page cache" in
general):
ARCH_HAS_CACHE_ALIASING -> ARCH_HAS_CPU_CACHE_ALIASING
dcache_is_aliasing() -> cpu_dcache_is_aliasing()
I noticed that you suggested "aliased" rather than "aliasing",
but I followed what arm64 did for icache_is_aliasing(). Do you
have a strong preference one way or another ?
Thanks,
Mathieu
On Wed, Jan 31, 2024 at 09:58:21AM -0500, Mathieu Desnoyers wrote:
> On 2024-01-30 21:48, Dave Chinner wrote:
> > On Tue, Jan 30, 2024 at 11:52:54AM -0500, Mathieu Desnoyers wrote:
> > > Introduce a generic way to query whether the dcache is virtually aliased
> > > on all architectures. Its purpose is to ensure that subsystems which
> > > are incompatible with virtually aliased data caches (e.g. FS_DAX) can
> > > reliably query this.
> > >
> > > For dcache aliasing, there are three scenarios dependending on the
> > > architecture. Here is a breakdown based on my understanding:
> > >
> > > A) The dcache is always aliasing:
> > >
> > > * arc
> > > * csky
> > > * m68k (note: shared memory mappings are incoherent ? SHMLBA is missing there.)
> > > * sh
> > > * parisc
> >
> > /me wonders why the dentry cache aliasing has problems on these
> > systems.
> >
> > Oh, dcache != fs/dcache.c (the VFS dentry cache).
> >
> > Can you please rename this function appropriately so us dumb
> > filesystem people don't confuse cpu data cache configurations with
> > the VFS dentry cache aliasing when we read this code? Something like
> > cpu_dcache_is_aliased(), perhaps?
>
> Good point, will do. I'm planning go rename as follows for v3 to
> eliminate confusion with dentry cache (and with "page cache" in
> general):
>
> ARCH_HAS_CACHE_ALIASING -> ARCH_HAS_CPU_CACHE_ALIASING
> dcache_is_aliasing() -> cpu_dcache_is_aliasing()
>
> I noticed that you suggested "aliased" rather than "aliasing",
> but I followed what arm64 did for icache_is_aliasing(). Do you
> have a strong preference one way or another ?
Not really.
-Dave.
@@ -6,6 +6,7 @@
config ARC
def_bool y
select ARC_TIMERS
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_CACHE_LINE_SIZE
select ARCH_HAS_DEBUG_VM_PGTABLE
select ARCH_HAS_DMA_PREP_COHERENT
new file mode 100644
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_ARC_CACHETYPE_H
+#define __ASM_ARC_CACHETYPE_H
+
+#include <linux/types.h>
+
+#define dcache_is_aliasing() true
+
+#endif
@@ -5,6 +5,7 @@ config ARM
select ARCH_32BIT_OFF_T
select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE if HAVE_KRETPROBES && FRAME_POINTER && !ARM_UNWIND
select ARCH_HAS_BINFMT_FLAT
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_CPU_FINALIZE_INIT if MMU
select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VIRTUAL if MMU
@@ -20,6 +20,8 @@ extern unsigned int cacheid;
#define icache_is_vipt_aliasing() cacheid_is(CACHEID_VIPT_I_ALIASING)
#define icache_is_pipt() cacheid_is(CACHEID_PIPT)
+#define dcache_is_aliasing() (cache_is_vivt() || cache_is_vipt_aliasing())
+
/*
* __LINUX_ARM_ARCH__ is the minimum supported CPU architecture
* Mask out support which will never be present on newer CPUs.
@@ -2,6 +2,7 @@
config CSKY
def_bool y
select ARCH_32BIT_OFF_T
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_DMA_PREP_COHERENT
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_SYNC_DMA_FOR_CPU
new file mode 100644
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_CSKY_CACHETYPE_H
+#define __ASM_CSKY_CACHETYPE_H
+
+#include <linux/types.h>
+
+#define dcache_is_aliasing() true
+
+#endif
@@ -3,6 +3,7 @@ config M68K
bool
default y
select ARCH_32BIT_OFF_T
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_BINFMT_FLAT
select ARCH_HAS_CPU_FINALIZE_INIT if MMU
select ARCH_HAS_CURRENT_STACK_POINTER
new file mode 100644
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_M68K_CACHETYPE_H
+#define __ASM_M68K_CACHETYPE_H
+
+#include <linux/types.h>
+
+#define dcache_is_aliasing() true
+
+#endif
@@ -4,6 +4,7 @@ config MIPS
default y
select ARCH_32BIT_OFF_T if !64BIT
select ARCH_BINFMT_ELF_STATE if MIPS_FP_SUPPORT
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_CPU_FINALIZE_INIT
select ARCH_HAS_CURRENT_STACK_POINTER if !CC_IS_CLANG || CLANG_VERSION >= 140000
select ARCH_HAS_DEBUG_VIRTUAL if !64BIT
new file mode 100644
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MIPS_CACHETYPE_H
+#define __ASM_MIPS_CACHETYPE_H
+
+#include <asm/cpu-features.h>
+
+#define dcache_is_aliasing() cpu_has_dc_aliases
+
+#endif
@@ -2,6 +2,7 @@
config NIOS2
def_bool y
select ARCH_32BIT_OFF_T
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_DMA_PREP_COHERENT
select ARCH_HAS_SYNC_DMA_FOR_CPU
select ARCH_HAS_SYNC_DMA_FOR_DEVICE
new file mode 100644
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_NIOS2_CACHETYPE_H
+#define __ASM_NIOS2_CACHETYPE_H
+
+#include <asm/page.h>
+#include <asm/cache.h>
+
+#define dcache_is_aliasing() (NIOS2_DCACHE_SIZE > PAGE_SIZE)
+
+#endif
@@ -8,6 +8,7 @@ config PARISC
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_SYSCALL_TRACEPOINTS
select ARCH_WANT_FRAME_POINTERS
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_DMA_ALLOC if PA11
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_STRICT_KERNEL_RWX
new file mode 100644
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_PARISC_CACHETYPE_H
+#define __ASM_PARISC_CACHETYPE_H
+
+#include <linux/types.h>
+
+#define dcache_is_aliasing() true
+
+#endif
@@ -2,6 +2,7 @@
config SUPERH
def_bool y
select ARCH_32BIT_OFF_T
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_ENABLE_MEMORY_HOTPLUG if SPARSEMEM && MMU
select ARCH_ENABLE_MEMORY_HOTREMOVE if SPARSEMEM && MMU
select ARCH_HAVE_NMI_SAFE_CMPXCHG if (GUSA_RB || CPU_SH4A)
new file mode 100644
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_SH_CACHETYPE_H
+#define __ASM_SH_CACHETYPE_H
+
+#include <linux/types.h>
+
+#define dcache_is_aliasing() true
+
+#endif
@@ -13,6 +13,7 @@ config 64BIT
config SPARC
bool
default y
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_MIGHT_HAVE_PC_PARPORT if SPARC64 && PCI
select ARCH_MIGHT_HAVE_PC_SERIO
select DMA_OPS
new file mode 100644
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_SPARC_CACHETYPE_H
+#define __ASM_SPARC_CACHETYPE_H
+
+#include <asm/page.h>
+
+#ifdef CONFIG_SPARC32
+extern int vac_cache_size;
+#define dcache_is_aliasing() (vac_cache_size > PAGE_SIZE)
+#else
+#define dcache_is_aliasing() (L1DCACHE_SIZE > PAGE_SIZE)
+#endif
+
+#endif
@@ -2,6 +2,7 @@
config XTENSA
def_bool y
select ARCH_32BIT_OFF_T
+ select ARCH_HAS_CACHE_ALIASING
select ARCH_HAS_BINFMT_FLAT if !MMU
select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VM_PGTABLE
new file mode 100644
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_XTENSA_CACHETYPE_H
+#define __ASM_XTENSA_CACHETYPE_H
+
+#include <asm/cache.h>
+#include <asm/page.h>
+
+#define dcache_is_aliasing() (DCACHE_WAY_SIZE > PAGE_SIZE)
+
+#endif
@@ -138,4 +138,10 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
#define use_arch_cache_info() (false)
#endif
+#ifndef CONFIG_ARCH_HAS_CACHE_ALIASING
+#define dcache_is_aliasing() false
+#else
+#include <asm/cachetype.h>
+#endif
+
#endif /* _LINUX_CACHEINFO_H */
@@ -1016,6 +1016,12 @@ config IDLE_PAGE_TRACKING
See Documentation/admin-guide/mm/idle_page_tracking.rst for
more details.
+# Architectures which implement dcache_is_aliasing() to query whether
+# the data caches are aliased (VIVT or VIPT with dcache aliasing) need
+# to select this.
+config ARCH_HAS_CACHE_ALIASING
+ bool
+
config ARCH_HAS_CACHE_LINE_SIZE
bool