[RFC PATCH 1/7] Introduce cache_is_aliasing() across all architectures

From: Mathieu Desnoyers
Date: Mon Jan 29 2024 - 16:07:47 EST

Next message: Mathieu Desnoyers: "[RFC PATCH 5/7] ext4: Use dax_is_supported()"
Previous message: Mathieu Desnoyers: "[RFC PATCH 0/7] Introduce cache_is_aliasing() to fix DAX regression"
In reply to: Mathieu Desnoyers: "[RFC PATCH 3/7] erofs: Use dax_is_supported()"
Next in thread: Mathieu Desnoyers: "[RFC PATCH 5/7] ext4: Use dax_is_supported()"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

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 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:
(ARCH_HAS_CACHE_ALIASING=y)

* arm V4, V5 (CPU_CACHE_VIVT)
* arc
* csky
* m68k (note: shared memory mappings are incoherent ? SHMLBA is missing there.)
* sh
* parisc

B) The dcache aliasing depends on querying CPU state at runtime:
(ARCH_HAS_CACHE_ALIASING_DYNAMIC=y)

* arm V6, V6K (CPU_CACHE_VIPT) (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:

* arm V7, V7M (unless ARM V6 or V6K are also present) (CPU_CACHE_VIPT)
* 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

Link: https://lore.kernel.org/lkml/20030910210416.GA24258@xxxxxxxxxxxxxxxxxx/
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: linux-cxl@xxxxxxxxxxxxxxx
Cc: nvdimm@xxxxxxxxxxxxxxx
---
arch/arc/Kconfig | 1 +
arch/arm/include/asm/cachetype.h | 3 +++
arch/arm/mm/Kconfig | 2 ++
arch/csky/Kconfig | 1 +
arch/m68k/Kconfig | 1 +
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/sh/Kconfig | 1 +
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 | 8 ++++++++
mm/Kconfig | 10 ++++++++++
17 files changed, 75 insertions(+)
create mode 100644 arch/mips/include/asm/cachetype.h
create mode 100644 arch/nios2/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/arm/include/asm/cachetype.h b/arch/arm/include/asm/cachetype.h
index e8c30430be33..b03054b35c74 100644
--- a/arch/arm/include/asm/cachetype.h
+++ b/arch/arm/include/asm/cachetype.h
@@ -16,6 +16,9 @@ extern unsigned int cacheid;
#define cache_is_vipt() cacheid_is(CACHEID_VIPT)
#define cache_is_vipt_nonaliasing() cacheid_is(CACHEID_VIPT_NONALIASING)
#define cache_is_vipt_aliasing() cacheid_is(CACHEID_VIPT_ALIASING)
+#ifdef CONFIG_ARCH_HAS_CACHE_ALIASING_DYNAMIC
+#define cache_is_aliasing() cache_is_vipt_aliasing()
+#endif
#define icache_is_vivt_asid_tagged() cacheid_is(CACHEID_ASID_TAGGED)
#define icache_is_vipt_aliasing() cacheid_is(CACHEID_VIPT_I_ALIASING)
#define icache_is_pipt() cacheid_is(CACHEID_PIPT)
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index c164cde50243..23af93cdc03d 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -539,9 +539,11 @@ config CPU_CACHE_NOP
bool

config CPU_CACHE_VIVT
+ select ARCH_HAS_CACHE_ALIASING
bool

config CPU_CACHE_VIPT
+ select ARCH_HAS_CACHE_ALIASING_DYNAMIC if CPU_V6 || CPU_V6K
bool

config CPU_CACHE_FA
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/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/mips/Kconfig b/arch/mips/Kconfig
index 797ae590ebdb..46981c507ceb 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_DYNAMIC
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..ce16ccde1841
--- /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 cache_is_aliasing() cpu_has_dc_aliases
+
+#endif
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index d54464021a61..949dcf99e147 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_DYNAMIC
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..f52a16cdb496
--- /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 cache_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/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/sparc/Kconfig b/arch/sparc/Kconfig
index 49849790e66d..a5edcbfaf6f8 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_DYNAMIC
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..8871e461cf23
--- /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 cache_is_aliasing() (vac_cache_size > PAGE_SIZE)
+#else
+#define cache_is_aliasing() (L1DCACHE_SIZE > PAGE_SIZE)
+#endif
+
+#endif
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 7d792077e5fd..ae99aa88595a 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_DYNAMIC
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..4329c885fe5f
--- /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 cache_is_aliasing() (DCACHE_WAY_SIZE > PAGE_SIZE)
+
+#endif
diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
index d504eb4b49ab..86f9a099fd5d 100644
--- a/include/linux/cacheinfo.h
+++ b/include/linux/cacheinfo.h
@@ -138,4 +138,12 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
#define use_arch_cache_info() (false)
#endif

+#ifdef CONFIG_ARCH_HAS_CACHE_ALIASING
+#define cache_is_aliasing() true
+#elif defined(CONFIG_ARCH_HAS_CACHE_ALIASING_DYNAMIC)
+#include <asm/cachetype.h>
+#else
+#define cache_is_aliasing() false
+#endif
+
#endif /* _LINUX_CACHEINFO_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index 57cd378c73d6..08f6ca0b465a 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1016,6 +1016,16 @@ config IDLE_PAGE_TRACKING
See Documentation/admin-guide/mm/idle_page_tracking.rst for
more details.

+# Architectures which alias the data cache (VIVT or VIPT with dcache
+# aliasing) need to select this.
+config ARCH_HAS_CACHE_ALIASING
+ bool
+
+# Architectures which need to query at runtime whether the data cache is
+# aliased need to select this.
+config ARCH_HAS_CACHE_ALIASING_DYNAMIC
+ bool
+
config ARCH_HAS_CACHE_LINE_SIZE
bool

--
2.39.2

Next message: Mathieu Desnoyers: "[RFC PATCH 5/7] ext4: Use dax_is_supported()"
Previous message: Mathieu Desnoyers: "[RFC PATCH 0/7] Introduce cache_is_aliasing() to fix DAX regression"
In reply to: Mathieu Desnoyers: "[RFC PATCH 3/7] erofs: Use dax_is_supported()"
Next in thread: Mathieu Desnoyers: "[RFC PATCH 5/7] ext4: Use dax_is_supported()"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]