[RFC PATCH v2 6/8] xfs: Use dax_is

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* [RFC PATCH v2 6/8] xfs: Use dax_is_supported()
       [not found] <20240130165255.212591-1-mathieu.desnoyers@efficios.com>
@ 2024-01-30 16:52 ` Mathieu Desnoyers
  2024-01-30 16:52 ` [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures Mathieu Desnoyers
  1 sibling, 0 replies; 5+ messages in thread
From: Mathieu Desnoyers @ 2024-01-30 16:52 UTC (permalink / raw)
  To: Dan Williams, Vishal Verma, Dave Jiang
  Cc: linux-kernel, Mathieu Desnoyers, Chandan Babu R, Darrick J . Wong,
	linux-xfs, Andrew Morton, Linus Torvalds, linux-mm, linux-arch,
	Matthew Wilcox, Arnd Bergmann, Russell King, nvdimm, linux-cxl

Use dax_is_supported() to validate whether the architecture has
virtually aliased data caches at mount time. Silently disable
DAX if dax=always is requested as a mount option on an architecture
which does not support DAX.

This is relevant for architectures which require a dynamic check
to validate whether they have virtually aliased data caches.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Chandan Babu R <chandan.babu@oracle.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org
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: nvdimm@lists.linux.dev
Cc: linux-cxl@vger.kernel.org
---
 fs/xfs/xfs_iops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index a0d77f5f512e..360f640159b0 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1208,7 +1208,7 @@ static bool
 xfs_inode_should_enable_dax(
 	struct xfs_inode *ip)
 {
-	if (!IS_ENABLED(CONFIG_FS_DAX))
+	if (!dax_is_supported())
 		return false;
 	if (xfs_has_dax_never(ip->i_mount))
 		return false;
-- 
2.39.2


^ permalink raw reply related	[flat|nested] 5+ messages in thread

* [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures
       [not found] <20240130165255.212591-1-mathieu.desnoyers@efficios.com>
  2024-01-30 16:52 ` [RFC PATCH v2 6/8] xfs: Use dax_is_supported() Mathieu Desnoyers
@ 2024-01-30 16:52 ` Mathieu Desnoyers
  2024-01-31  2:48   ` Dave Chinner
  1 sibling, 1 reply; 5+ messages in thread
From: Mathieu Desnoyers @ 2024-01-30 16:52 UTC (permalink / raw)
  To: Dan Williams, Vishal Verma, Dave Jiang
  Cc: linux-kernel, Mathieu Desnoyers, Andrew Morton, Linus Torvalds,
	linux-mm, linux-arch, Matthew Wilcox, Arnd Bergmann, Russell King,
	linux-cxl, nvdimm, linux-xfs

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

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 1b0483c51cc1..969e6740bcf7 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -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
diff --git a/arch/arc/include/asm/cachetype.h b/arch/arc/include/asm/cachetype.h
new file mode 100644
index 000000000000..290e3cc85845
--- /dev/null
+++ b/arch/arc/include/asm/cachetype.h
@@ -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
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f8567e95f98b..5adeee5e421f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -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
diff --git a/arch/arm/include/asm/cachetype.h b/arch/arm/include/asm/cachetype.h
index e8c30430be33..18311570d4f0 100644
--- a/arch/arm/include/asm/cachetype.h
+++ b/arch/arm/include/asm/cachetype.h
@@ -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.
diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index cf2a6fd7dff8..439d7640deb8 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -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
diff --git a/arch/csky/include/asm/cachetype.h b/arch/csky/include/asm/cachetype.h
new file mode 100644
index 000000000000..fd21c815a8e4
--- /dev/null
+++ b/arch/csky/include/asm/cachetype.h
@@ -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
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 4b3e93cac723..216338704f0a 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -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
diff --git a/arch/m68k/include/asm/cachetype.h b/arch/m68k/include/asm/cachetype.h
new file mode 100644
index 000000000000..24298a45b215
--- /dev/null
+++ b/arch/m68k/include/asm/cachetype.h
@@ -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
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 797ae590ebdb..cc21e88b2dc4 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -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
diff --git a/arch/mips/include/asm/cachetype.h b/arch/mips/include/asm/cachetype.h
new file mode 100644
index 000000000000..b967c4219c31
--- /dev/null
+++ b/arch/mips/include/asm/cachetype.h
@@ -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
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index d54464021a61..af3a0631f4f1 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -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
diff --git a/arch/nios2/include/asm/cachetype.h b/arch/nios2/include/asm/cachetype.h
new file mode 100644
index 000000000000..3027ba4e75ab
--- /dev/null
+++ b/arch/nios2/include/asm/cachetype.h
@@ -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
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index d14ccc948a29..e8c217744d83 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -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
diff --git a/arch/parisc/include/asm/cachetype.h b/arch/parisc/include/asm/cachetype.h
new file mode 100644
index 000000000000..a7f49ff26e3f
--- /dev/null
+++ b/arch/parisc/include/asm/cachetype.h
@@ -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
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 7500521b2b98..6465ef80c055 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -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)
diff --git a/arch/sh/include/asm/cachetype.h b/arch/sh/include/asm/cachetype.h
new file mode 100644
index 000000000000..55619e60c55f
--- /dev/null
+++ b/arch/sh/include/asm/cachetype.h
@@ -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
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 49849790e66d..8794e0d0920f 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -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
diff --git a/arch/sparc/include/asm/cachetype.h b/arch/sparc/include/asm/cachetype.h
new file mode 100644
index 000000000000..3ebc0e08a298
--- /dev/null
+++ b/arch/sparc/include/asm/cachetype.h
@@ -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
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 7d792077e5fd..54dbe9f42ec0 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -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
diff --git a/arch/xtensa/include/asm/cachetype.h b/arch/xtensa/include/asm/cachetype.h
new file mode 100644
index 000000000000..1de9337e9dbd
--- /dev/null
+++ b/arch/xtensa/include/asm/cachetype.h
@@ -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
diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
index d504eb4b49ab..a307916fac40 100644
--- a/include/linux/cacheinfo.h
+++ b/include/linux/cacheinfo.h
@@ -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 */
diff --git a/mm/Kconfig b/mm/Kconfig
index 57cd378c73d6..3fa87e45883d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -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
 
-- 
2.39.2


^ permalink raw reply related	[flat|nested] 5+ messages in thread

* Re: [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures
  2024-01-30 16:52 ` [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures Mathieu Desnoyers
@ 2024-01-31  2:48   ` Dave Chinner
  2024-01-31 14:58     ` Mathieu Desnoyers
  0 siblings, 1 reply; 5+ messages in thread
From: Dave Chinner @ 2024-01-31  2:48 UTC (permalink / raw)
  To: Mathieu Desnoyers
  Cc: Dan Williams, Vishal Verma, Dave Jiang, linux-kernel,
	Andrew Morton, Linus Torvalds, linux-mm, linux-arch,
	Matthew Wilcox, Arnd Bergmann, Russell King, linux-cxl, nvdimm,
	linux-xfs

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.
-- 
Dave Chinner
david@fromorbit.com

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures
  2024-01-31  2:48   ` Dave Chinner
@ 2024-01-31 14:58     ` Mathieu Desnoyers
  2024-01-31 20:42       ` Dave Chinner
  0 siblings, 1 reply; 5+ messages in thread
From: Mathieu Desnoyers @ 2024-01-31 14:58 UTC (permalink / raw)
  To: Dave Chinner
  Cc: Dan Williams, Vishal Verma, Dave Jiang, linux-kernel,
	Andrew Morton, Linus Torvalds, linux-mm, linux-arch,
	Matthew Wilcox, Arnd Bergmann, Russell King, linux-cxl, nvdimm,
	linux-xfs

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

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures
  2024-01-31 14:58     ` Mathieu Desnoyers
@ 2024-01-31 20:42       ` Dave Chinner
  0 siblings, 0 replies; 5+ messages in thread
From: Dave Chinner @ 2024-01-31 20:42 UTC (permalink / raw)
  To: Mathieu Desnoyers
  Cc: Dan Williams, Vishal Verma, Dave Jiang, linux-kernel,
	Andrew Morton, Linus Torvalds, linux-mm, linux-arch,
	Matthew Wilcox, Arnd Bergmann, Russell King, linux-cxl, nvdimm,
	linux-xfs

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.
-- 
Dave Chinner
david@fromorbit.com

^ permalink raw reply	[flat|nested] 5+ messages in thread

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2024-01-30 16:52 ` [RFC PATCH v2 6/8] xfs: Use dax_is_supported() Mathieu Desnoyers
2024-01-30 16:52 ` [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures Mathieu Desnoyers
2024-01-31  2:48   ` Dave Chinner
2024-01-31 14:58     ` Mathieu Desnoyers
2024-01-31 20:42       ` Dave Chinner

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