When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum
slab alignment to 16. This happens even if MTE is not supported in
hardware or disabled via kasan=off, which creates an unnecessary
memory overhead in those cases. Eliminate this overhead by making
the minimum slab alignment a runtime property and only aligning to
16 if KASAN is enabled at runtime.
On a DragonBoard 845c (non-MTE hardware) with a kernel built with
CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android
boot I see the following Slab measurements in /proc/meminfo (median
of 3 reboots):
Before: 169020 kB
After: 167304 kB
Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead
Signed-off-by: Peter Collingbourne <[email protected]>
---
v2:
- use max instead of max_t in flat_stack_align()
arch/arc/include/asm/cache.h | 4 ++--
arch/arm/include/asm/cache.h | 2 +-
arch/arm64/include/asm/cache.h | 19 +++++++++++++------
arch/microblaze/include/asm/page.h | 2 +-
arch/riscv/include/asm/cache.h | 2 +-
arch/sparc/include/asm/cache.h | 2 +-
arch/xtensa/include/asm/processor.h | 2 +-
fs/binfmt_flat.c | 9 ++++++---
include/crypto/hash.h | 2 +-
include/linux/slab.h | 22 +++++++++++++++++-----
mm/slab.c | 7 +++----
mm/slab_common.c | 3 +--
mm/slob.c | 6 +++---
13 files changed, 51 insertions(+), 31 deletions(-)
diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h
index f0f1fc5d62b6..b6a7763fd5d6 100644
--- a/arch/arc/include/asm/cache.h
+++ b/arch/arc/include/asm/cache.h
@@ -55,11 +55,11 @@
* Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses
* ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit
* alignment for any atomic64_t embedded in buffer.
- * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed
+ * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed
* value of 4 (and not 8) in ARC ABI.
*/
#if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC)
-#define ARCH_SLAB_MINALIGN 8
+#define ARCH_SLAB_MIN_MINALIGN 8
#endif
extern int ioc_enable;
diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h
index e3ea34558ada..3e1018bb9805 100644
--- a/arch/arm/include/asm/cache.h
+++ b/arch/arm/include/asm/cache.h
@@ -21,7 +21,7 @@
* With EABI on ARMv5 and above we must have 64-bit aligned slab pointers.
*/
#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
-#define ARCH_SLAB_MINALIGN 8
+#define ARCH_SLAB_MIN_MINALIGN 8
#endif
#define __read_mostly __section(".data..read_mostly")
diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
index a074459f8f2f..38f171591c3f 100644
--- a/arch/arm64/include/asm/cache.h
+++ b/arch/arm64/include/asm/cache.h
@@ -6,6 +6,7 @@
#define __ASM_CACHE_H
#include <asm/cputype.h>
+#include <asm/mte-def.h>
#define CTR_L1IP_SHIFT 14
#define CTR_L1IP_MASK 3
@@ -49,15 +50,21 @@
*/
#define ARCH_DMA_MINALIGN (128)
-#ifdef CONFIG_KASAN_SW_TAGS
-#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
-#elif defined(CONFIG_KASAN_HW_TAGS)
-#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE
-#endif
-
#ifndef __ASSEMBLY__
#include <linux/bitops.h>
+#include <linux/kasan-enabled.h>
+
+#ifdef CONFIG_KASAN_SW_TAGS
+#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
+#elif defined(CONFIG_KASAN_HW_TAGS)
+static inline size_t arch_slab_minalign(void)
+{
+ return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE :
+ __alignof__(unsigned long long);
+}
+#define arch_slab_minalign() arch_slab_minalign()
+#endif
#define ICACHEF_ALIASING 0
#define ICACHEF_VPIPT 1
diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h
index 4b8b2fa78fc5..ccdbc1da3c3e 100644
--- a/arch/microblaze/include/asm/page.h
+++ b/arch/microblaze/include/asm/page.h
@@ -33,7 +33,7 @@
/* MS be sure that SLAB allocates aligned objects */
#define ARCH_DMA_MINALIGN L1_CACHE_BYTES
-#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES
+#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES
/*
* PAGE_OFFSET -- the first address of the first page of memory. With MMU
diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h
index 9b58b104559e..7beb3b5d27c7 100644
--- a/arch/riscv/include/asm/cache.h
+++ b/arch/riscv/include/asm/cache.h
@@ -16,7 +16,7 @@
* the flat loader aligns it accordingly.
*/
#ifndef CONFIG_MMU
-#define ARCH_SLAB_MINALIGN 16
+#define ARCH_SLAB_MIN_MINALIGN 16
#endif
#endif /* _ASM_RISCV_CACHE_H */
diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h
index e62fd0e72606..9d8cb4687b7e 100644
--- a/arch/sparc/include/asm/cache.h
+++ b/arch/sparc/include/asm/cache.h
@@ -8,7 +8,7 @@
#ifndef _SPARC_CACHE_H
#define _SPARC_CACHE_H
-#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
+#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
#define L1_CACHE_SHIFT 5
#define L1_CACHE_BYTES 32
diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h
index 4489a27d527a..e3ea278e3fcf 100644
--- a/arch/xtensa/include/asm/processor.h
+++ b/arch/xtensa/include/asm/processor.h
@@ -18,7 +18,7 @@
#include <asm/types.h>
#include <asm/regs.h>
-#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT
+#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT
/*
* User space process size: 1 GB.
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index 626898150011..23ce3439eafa 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -64,7 +64,10 @@
* Here we can be a bit looser than the data sections since this
* needs to only meet arch ABI requirements.
*/
-#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN)
+static size_t flat_stack_align(void)
+{
+ return max(sizeof(void *), arch_slab_minalign());
+}
#define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */
#define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */
@@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start
sp -= 2; /* argvp + envp */
sp -= 1; /* &argc */
- current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN;
+ current->mm->start_stack = (unsigned long)sp & -flat_stack_align();
sp = (unsigned long __user *)current->mm->start_stack;
if (put_user(bprm->argc, sp++))
@@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
#endif
stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */
stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */
- stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN);
+ stack_len = ALIGN(stack_len, flat_stack_align());
res = load_flat_file(bprm, &libinfo, 0, &stack_len);
if (res < 0)
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index f140e4643949..442c290f458c 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -149,7 +149,7 @@ struct ahash_alg {
struct shash_desc {
struct crypto_shash *tfm;
- void *__ctx[] __aligned(ARCH_SLAB_MINALIGN);
+ void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN);
};
#define HASH_MAX_DIGESTSIZE 64
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 373b3ef99f4e..80e517593372 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -201,21 +201,33 @@ void kmem_dump_obj(void *object);
#endif
/*
- * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
+ * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment.
* Intended for arches that get misalignment faults even for 64 bit integer
* aligned buffers.
*/
-#ifndef ARCH_SLAB_MINALIGN
-#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
+#ifndef ARCH_SLAB_MIN_MINALIGN
+#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
+#endif
+
+/*
+ * Arches can define this function if they want to decide the minimum slab
+ * alignment at runtime. The value returned by the function must be
+ * >= ARCH_SLAB_MIN_MINALIGN.
+ */
+#ifndef arch_slab_minalign
+static inline size_t arch_slab_minalign(void)
+{
+ return ARCH_SLAB_MIN_MINALIGN;
+}
#endif
/*
* kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
- * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN
+ * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN
* aligned pointers.
*/
#define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN)
-#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN)
+#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN)
#define __assume_page_alignment __assume_aligned(PAGE_SIZE)
/*
diff --git a/mm/slab.c b/mm/slab.c
index 0edb474edef1..97b756976c8b 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3009,10 +3009,9 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
objp += obj_offset(cachep);
if (cachep->ctor && cachep->flags & SLAB_POISON)
cachep->ctor(objp);
- if (ARCH_SLAB_MINALIGN &&
- ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))) {
- pr_err("0x%px: not aligned to ARCH_SLAB_MINALIGN=%d\n",
- objp, (int)ARCH_SLAB_MINALIGN);
+ if ((unsigned long)objp & (arch_slab_minalign() - 1)) {
+ pr_err("0x%px: not aligned to arch_slab_minalign()=%d\n", objp,
+ (int)arch_slab_minalign());
}
return objp;
}
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 2b3206a2c3b5..33cc49810a54 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -154,8 +154,7 @@ static unsigned int calculate_alignment(slab_flags_t flags,
align = max(align, ralign);
}
- if (align < ARCH_SLAB_MINALIGN)
- align = ARCH_SLAB_MINALIGN;
+ align = max_t(size_t, align, arch_slab_minalign());
return ALIGN(align, sizeof(void *));
}
diff --git a/mm/slob.c b/mm/slob.c
index 40ea6e2d4ccd..3bd2669bd690 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -478,7 +478,7 @@ static __always_inline void *
__do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
{
unsigned int *m;
- int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+ int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
void *ret;
gfp &= gfp_allowed_mask;
@@ -555,7 +555,7 @@ void kfree(const void *block)
sp = virt_to_folio(block);
if (folio_test_slab(sp)) {
- int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+ int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
unsigned int *m = (unsigned int *)(block - align);
slob_free(m, *m + align);
} else {
@@ -584,7 +584,7 @@ size_t __ksize(const void *block)
if (unlikely(!folio_test_slab(folio)))
return folio_size(folio);
- align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+ align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
m = (unsigned int *)(block - align);
return SLOB_UNITS(*m) * SLOB_UNIT;
}
--
2.36.0.rc2.479.g8af0fa9b8e-goog
On Thu, Apr 21, 2022 at 11:16 PM Peter Collingbourne <[email protected]> wrote:
>
> When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum
> slab alignment to 16. This happens even if MTE is not supported in
> hardware or disabled via kasan=off, which creates an unnecessary
> memory overhead in those cases. Eliminate this overhead by making
> the minimum slab alignment a runtime property and only aligning to
> 16 if KASAN is enabled at runtime.
>
> On a DragonBoard 845c (non-MTE hardware) with a kernel built with
> CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android
> boot I see the following Slab measurements in /proc/meminfo (median
> of 3 reboots):
>
> Before: 169020 kB
> After: 167304 kB
Thanks for the improvement, Peter!
Overall, the patch looks good to me:
Reviewed-by: Andrey Konovalov <[email protected]>
While looking at the code, I noticed a couple of issues in the already
existing comments. Not sure if they are worth fixing, but I'll point
them out just in case.
> Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead
> Signed-off-by: Peter Collingbourne <[email protected]>
> ---
> v2:
> - use max instead of max_t in flat_stack_align()
>
> arch/arc/include/asm/cache.h | 4 ++--
> arch/arm/include/asm/cache.h | 2 +-
> arch/arm64/include/asm/cache.h | 19 +++++++++++++------
> arch/microblaze/include/asm/page.h | 2 +-
> arch/riscv/include/asm/cache.h | 2 +-
> arch/sparc/include/asm/cache.h | 2 +-
> arch/xtensa/include/asm/processor.h | 2 +-
> fs/binfmt_flat.c | 9 ++++++---
> include/crypto/hash.h | 2 +-
> include/linux/slab.h | 22 +++++++++++++++++-----
> mm/slab.c | 7 +++----
> mm/slab_common.c | 3 +--
> mm/slob.c | 6 +++---
> 13 files changed, 51 insertions(+), 31 deletions(-)
>
> diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h
> index f0f1fc5d62b6..b6a7763fd5d6 100644
> --- a/arch/arc/include/asm/cache.h
> +++ b/arch/arc/include/asm/cache.h
> @@ -55,11 +55,11 @@
> * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses
> * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit
> * alignment for any atomic64_t embedded in buffer.
> - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed
> + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed
> * value of 4 (and not 8) in ARC ABI.
> */
> #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC)
> -#define ARCH_SLAB_MINALIGN 8
> +#define ARCH_SLAB_MIN_MINALIGN 8
> #endif
>
> extern int ioc_enable;
> diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h
> index e3ea34558ada..3e1018bb9805 100644
> --- a/arch/arm/include/asm/cache.h
> +++ b/arch/arm/include/asm/cache.h
> @@ -21,7 +21,7 @@
> * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers.
> */
> #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
> -#define ARCH_SLAB_MINALIGN 8
> +#define ARCH_SLAB_MIN_MINALIGN 8
> #endif
>
> #define __read_mostly __section(".data..read_mostly")
> diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
> index a074459f8f2f..38f171591c3f 100644
> --- a/arch/arm64/include/asm/cache.h
> +++ b/arch/arm64/include/asm/cache.h
> @@ -6,6 +6,7 @@
> #define __ASM_CACHE_H
>
> #include <asm/cputype.h>
> +#include <asm/mte-def.h>
>
> #define CTR_L1IP_SHIFT 14
> #define CTR_L1IP_MASK 3
> @@ -49,15 +50,21 @@
> */
> #define ARCH_DMA_MINALIGN (128)
>
> -#ifdef CONFIG_KASAN_SW_TAGS
> -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
> -#elif defined(CONFIG_KASAN_HW_TAGS)
> -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE
> -#endif
> -
> #ifndef __ASSEMBLY__
>
> #include <linux/bitops.h>
> +#include <linux/kasan-enabled.h>
> +
> +#ifdef CONFIG_KASAN_SW_TAGS
> +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
> +#elif defined(CONFIG_KASAN_HW_TAGS)
> +static inline size_t arch_slab_minalign(void)
> +{
> + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE :
> + __alignof__(unsigned long long);
> +}
> +#define arch_slab_minalign() arch_slab_minalign()
> +#endif
>
> #define ICACHEF_ALIASING 0
> #define ICACHEF_VPIPT 1
> diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h
> index 4b8b2fa78fc5..ccdbc1da3c3e 100644
> --- a/arch/microblaze/include/asm/page.h
> +++ b/arch/microblaze/include/asm/page.h
> @@ -33,7 +33,7 @@
> /* MS be sure that SLAB allocates aligned objects */
> #define ARCH_DMA_MINALIGN L1_CACHE_BYTES
>
> -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES
> +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES
>
> /*
> * PAGE_OFFSET -- the first address of the first page of memory. With MMU
> diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h
> index 9b58b104559e..7beb3b5d27c7 100644
> --- a/arch/riscv/include/asm/cache.h
> +++ b/arch/riscv/include/asm/cache.h
> @@ -16,7 +16,7 @@
> * the flat loader aligns it accordingly.
> */
> #ifndef CONFIG_MMU
> -#define ARCH_SLAB_MINALIGN 16
> +#define ARCH_SLAB_MIN_MINALIGN 16
> #endif
>
> #endif /* _ASM_RISCV_CACHE_H */
> diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h
> index e62fd0e72606..9d8cb4687b7e 100644
> --- a/arch/sparc/include/asm/cache.h
> +++ b/arch/sparc/include/asm/cache.h
> @@ -8,7 +8,7 @@
> #ifndef _SPARC_CACHE_H
> #define _SPARC_CACHE_H
>
> -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
>
> #define L1_CACHE_SHIFT 5
> #define L1_CACHE_BYTES 32
> diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h
> index 4489a27d527a..e3ea278e3fcf 100644
> --- a/arch/xtensa/include/asm/processor.h
> +++ b/arch/xtensa/include/asm/processor.h
> @@ -18,7 +18,7 @@
> #include <asm/types.h>
> #include <asm/regs.h>
>
> -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT
> +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT
>
> /*
> * User space process size: 1 GB.
> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
> index 626898150011..23ce3439eafa 100644
> --- a/fs/binfmt_flat.c
> +++ b/fs/binfmt_flat.c
> @@ -64,7 +64,10 @@
> * Here we can be a bit looser than the data sections since this
> * needs to only meet arch ABI requirements.
> */
> -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN)
> +static size_t flat_stack_align(void)
> +{
> + return max(sizeof(void *), arch_slab_minalign());
> +}
>
> #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */
> #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */
> @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start
> sp -= 2; /* argvp + envp */
> sp -= 1; /* &argc */
>
> - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN;
> + current->mm->start_stack = (unsigned long)sp & -flat_stack_align();
> sp = (unsigned long __user *)current->mm->start_stack;
>
> if (put_user(bprm->argc, sp++))
> @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
> #endif
> stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */
> stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */
> - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN);
> + stack_len = ALIGN(stack_len, flat_stack_align());
>
> res = load_flat_file(bprm, &libinfo, 0, &stack_len);
> if (res < 0)
> diff --git a/include/crypto/hash.h b/include/crypto/hash.h
> index f140e4643949..442c290f458c 100644
> --- a/include/crypto/hash.h
> +++ b/include/crypto/hash.h
> @@ -149,7 +149,7 @@ struct ahash_alg {
>
> struct shash_desc {
> struct crypto_shash *tfm;
> - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN);
> + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN);
> };
>
> #define HASH_MAX_DIGESTSIZE 64
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 373b3ef99f4e..80e517593372 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object);
> #endif
>
> /*
> - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
> + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment.
> * Intended for arches that get misalignment faults even for 64 bit integer
> * aligned buffers.
> */
> -#ifndef ARCH_SLAB_MINALIGN
> -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> +#ifndef ARCH_SLAB_MIN_MINALIGN
> +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
> +#endif
> +
> +/*
> + * Arches can define this function if they want to decide the minimum slab
> + * alignment at runtime. The value returned by the function must be
> + * >= ARCH_SLAB_MIN_MINALIGN.
> + */
> +#ifndef arch_slab_minalign
> +static inline size_t arch_slab_minalign(void)
> +{
> + return ARCH_SLAB_MIN_MINALIGN;
> +}
> #endif
>
> /*
> * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
> - * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN
> + * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN
> * aligned pointers.
This comment is not precise: kmalloc relies on kmem_cache_alloc, so
kmalloc technically returns pointers aligned to
max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MIN_MINALIGN). See
create_kmalloc_cache()->create_boot_cache()->calculate_alignment() for
SLAB and SLUB and __do_kmalloc_node() for SLOB. This alignment is
stronger than the one is specified for __assume_kmalloc_alignment
below, so the code should be fine. However, the comment is confusing.
Also, the comment next to the ARCH_KMALLOC_MINALIGN definition says
"Setting ARCH_KMALLOC_MINALIGN in arch headers" while it should say
"Setting ARCH_DMA_MINALIGN in arch headers".
> */
> #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN)
> -#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN)
> +#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN)
> #define __assume_page_alignment __assume_aligned(PAGE_SIZE)
>
> /*
> diff --git a/mm/slab.c b/mm/slab.c
> index 0edb474edef1..97b756976c8b 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3009,10 +3009,9 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
> objp += obj_offset(cachep);
> if (cachep->ctor && cachep->flags & SLAB_POISON)
> cachep->ctor(objp);
> - if (ARCH_SLAB_MINALIGN &&
> - ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))) {
> - pr_err("0x%px: not aligned to ARCH_SLAB_MINALIGN=%d\n",
> - objp, (int)ARCH_SLAB_MINALIGN);
> + if ((unsigned long)objp & (arch_slab_minalign() - 1)) {
> + pr_err("0x%px: not aligned to arch_slab_minalign()=%d\n", objp,
> + (int)arch_slab_minalign());
> }
> return objp;
> }
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 2b3206a2c3b5..33cc49810a54 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -154,8 +154,7 @@ static unsigned int calculate_alignment(slab_flags_t flags,
> align = max(align, ralign);
> }
>
> - if (align < ARCH_SLAB_MINALIGN)
> - align = ARCH_SLAB_MINALIGN;
> + align = max_t(size_t, align, arch_slab_minalign());
>
> return ALIGN(align, sizeof(void *));
> }
> diff --git a/mm/slob.c b/mm/slob.c
> index 40ea6e2d4ccd..3bd2669bd690 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -478,7 +478,7 @@ static __always_inline void *
> __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
> {
> unsigned int *m;
> - int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
> + int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
> void *ret;
>
> gfp &= gfp_allowed_mask;
> @@ -555,7 +555,7 @@ void kfree(const void *block)
>
> sp = virt_to_folio(block);
> if (folio_test_slab(sp)) {
> - int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
> + int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
> unsigned int *m = (unsigned int *)(block - align);
> slob_free(m, *m + align);
> } else {
> @@ -584,7 +584,7 @@ size_t __ksize(const void *block)
> if (unlikely(!folio_test_slab(folio)))
> return folio_size(folio);
>
> - align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
> + align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
> m = (unsigned int *)(block - align);
> return SLOB_UNITS(*m) * SLOB_UNIT;
> }
> --
> 2.36.0.rc2.479.g8af0fa9b8e-goog
>
On Thu, Apr 21, 2022 at 02:15:48PM -0700, Peter Collingbourne wrote:
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 373b3ef99f4e..80e517593372 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object);
> #endif
>
> /*
> - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
> + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment.
> * Intended for arches that get misalignment faults even for 64 bit integer
> * aligned buffers.
> */
> -#ifndef ARCH_SLAB_MINALIGN
> -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> +#ifndef ARCH_SLAB_MIN_MINALIGN
> +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
> +#endif
Sorry, only a drive-by comment, I'll look at the arm64 parts next week.
I've seen it mentioned in the first version, what's the point of MIN_MIN
and not just MIN?
--
Catalin
On Fri, Apr 22, 2022 at 9:04 AM Andrey Konovalov <[email protected]> wrote:
>
> On Thu, Apr 21, 2022 at 11:16 PM Peter Collingbourne <[email protected]> wrote:
> >
> > When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum
> > slab alignment to 16. This happens even if MTE is not supported in
> > hardware or disabled via kasan=off, which creates an unnecessary
> > memory overhead in those cases. Eliminate this overhead by making
> > the minimum slab alignment a runtime property and only aligning to
> > 16 if KASAN is enabled at runtime.
> >
> > On a DragonBoard 845c (non-MTE hardware) with a kernel built with
> > CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android
> > boot I see the following Slab measurements in /proc/meminfo (median
> > of 3 reboots):
> >
> > Before: 169020 kB
> > After: 167304 kB
>
> Thanks for the improvement, Peter!
>
> Overall, the patch looks good to me:
>
> Reviewed-by: Andrey Konovalov <[email protected]>
Thanks!
> While looking at the code, I noticed a couple of issues in the already
> existing comments. Not sure if they are worth fixing, but I'll point
> them out just in case.
>
> > Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead
> > Signed-off-by: Peter Collingbourne <[email protected]>
> > ---
> > v2:
> > - use max instead of max_t in flat_stack_align()
> >
> > arch/arc/include/asm/cache.h | 4 ++--
> > arch/arm/include/asm/cache.h | 2 +-
> > arch/arm64/include/asm/cache.h | 19 +++++++++++++------
> > arch/microblaze/include/asm/page.h | 2 +-
> > arch/riscv/include/asm/cache.h | 2 +-
> > arch/sparc/include/asm/cache.h | 2 +-
> > arch/xtensa/include/asm/processor.h | 2 +-
> > fs/binfmt_flat.c | 9 ++++++---
> > include/crypto/hash.h | 2 +-
> > include/linux/slab.h | 22 +++++++++++++++++-----
> > mm/slab.c | 7 +++----
> > mm/slab_common.c | 3 +--
> > mm/slob.c | 6 +++---
> > 13 files changed, 51 insertions(+), 31 deletions(-)
> >
> > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h
> > index f0f1fc5d62b6..b6a7763fd5d6 100644
> > --- a/arch/arc/include/asm/cache.h
> > +++ b/arch/arc/include/asm/cache.h
> > @@ -55,11 +55,11 @@
> > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses
> > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit
> > * alignment for any atomic64_t embedded in buffer.
> > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed
> > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed
> > * value of 4 (and not 8) in ARC ABI.
> > */
> > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC)
> > -#define ARCH_SLAB_MINALIGN 8
> > +#define ARCH_SLAB_MIN_MINALIGN 8
> > #endif
> >
> > extern int ioc_enable;
> > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h
> > index e3ea34558ada..3e1018bb9805 100644
> > --- a/arch/arm/include/asm/cache.h
> > +++ b/arch/arm/include/asm/cache.h
> > @@ -21,7 +21,7 @@
> > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers.
> > */
> > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
> > -#define ARCH_SLAB_MINALIGN 8
> > +#define ARCH_SLAB_MIN_MINALIGN 8
> > #endif
> >
> > #define __read_mostly __section(".data..read_mostly")
> > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
> > index a074459f8f2f..38f171591c3f 100644
> > --- a/arch/arm64/include/asm/cache.h
> > +++ b/arch/arm64/include/asm/cache.h
> > @@ -6,6 +6,7 @@
> > #define __ASM_CACHE_H
> >
> > #include <asm/cputype.h>
> > +#include <asm/mte-def.h>
> >
> > #define CTR_L1IP_SHIFT 14
> > #define CTR_L1IP_MASK 3
> > @@ -49,15 +50,21 @@
> > */
> > #define ARCH_DMA_MINALIGN (128)
> >
> > -#ifdef CONFIG_KASAN_SW_TAGS
> > -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
> > -#elif defined(CONFIG_KASAN_HW_TAGS)
> > -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE
> > -#endif
> > -
> > #ifndef __ASSEMBLY__
> >
> > #include <linux/bitops.h>
> > +#include <linux/kasan-enabled.h>
> > +
> > +#ifdef CONFIG_KASAN_SW_TAGS
> > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
> > +#elif defined(CONFIG_KASAN_HW_TAGS)
> > +static inline size_t arch_slab_minalign(void)
> > +{
> > + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE :
> > + __alignof__(unsigned long long);
> > +}
> > +#define arch_slab_minalign() arch_slab_minalign()
> > +#endif
> >
> > #define ICACHEF_ALIASING 0
> > #define ICACHEF_VPIPT 1
> > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h
> > index 4b8b2fa78fc5..ccdbc1da3c3e 100644
> > --- a/arch/microblaze/include/asm/page.h
> > +++ b/arch/microblaze/include/asm/page.h
> > @@ -33,7 +33,7 @@
> > /* MS be sure that SLAB allocates aligned objects */
> > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES
> >
> > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES
> > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES
> >
> > /*
> > * PAGE_OFFSET -- the first address of the first page of memory. With MMU
> > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h
> > index 9b58b104559e..7beb3b5d27c7 100644
> > --- a/arch/riscv/include/asm/cache.h
> > +++ b/arch/riscv/include/asm/cache.h
> > @@ -16,7 +16,7 @@
> > * the flat loader aligns it accordingly.
> > */
> > #ifndef CONFIG_MMU
> > -#define ARCH_SLAB_MINALIGN 16
> > +#define ARCH_SLAB_MIN_MINALIGN 16
> > #endif
> >
> > #endif /* _ASM_RISCV_CACHE_H */
> > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h
> > index e62fd0e72606..9d8cb4687b7e 100644
> > --- a/arch/sparc/include/asm/cache.h
> > +++ b/arch/sparc/include/asm/cache.h
> > @@ -8,7 +8,7 @@
> > #ifndef _SPARC_CACHE_H
> > #define _SPARC_CACHE_H
> >
> > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
> >
> > #define L1_CACHE_SHIFT 5
> > #define L1_CACHE_BYTES 32
> > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h
> > index 4489a27d527a..e3ea278e3fcf 100644
> > --- a/arch/xtensa/include/asm/processor.h
> > +++ b/arch/xtensa/include/asm/processor.h
> > @@ -18,7 +18,7 @@
> > #include <asm/types.h>
> > #include <asm/regs.h>
> >
> > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT
> > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT
> >
> > /*
> > * User space process size: 1 GB.
> > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
> > index 626898150011..23ce3439eafa 100644
> > --- a/fs/binfmt_flat.c
> > +++ b/fs/binfmt_flat.c
> > @@ -64,7 +64,10 @@
> > * Here we can be a bit looser than the data sections since this
> > * needs to only meet arch ABI requirements.
> > */
> > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN)
> > +static size_t flat_stack_align(void)
> > +{
> > + return max(sizeof(void *), arch_slab_minalign());
> > +}
> >
> > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */
> > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */
> > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start
> > sp -= 2; /* argvp + envp */
> > sp -= 1; /* &argc */
> >
> > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN;
> > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align();
> > sp = (unsigned long __user *)current->mm->start_stack;
> >
> > if (put_user(bprm->argc, sp++))
> > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
> > #endif
> > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */
> > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */
> > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN);
> > + stack_len = ALIGN(stack_len, flat_stack_align());
> >
> > res = load_flat_file(bprm, &libinfo, 0, &stack_len);
> > if (res < 0)
> > diff --git a/include/crypto/hash.h b/include/crypto/hash.h
> > index f140e4643949..442c290f458c 100644
> > --- a/include/crypto/hash.h
> > +++ b/include/crypto/hash.h
> > @@ -149,7 +149,7 @@ struct ahash_alg {
> >
> > struct shash_desc {
> > struct crypto_shash *tfm;
> > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN);
> > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN);
> > };
> >
> > #define HASH_MAX_DIGESTSIZE 64
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 373b3ef99f4e..80e517593372 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object);
> > #endif
> >
> > /*
> > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
> > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment.
> > * Intended for arches that get misalignment faults even for 64 bit integer
> > * aligned buffers.
> > */
> > -#ifndef ARCH_SLAB_MINALIGN
> > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> > +#ifndef ARCH_SLAB_MIN_MINALIGN
> > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
> > +#endif
> > +
> > +/*
> > + * Arches can define this function if they want to decide the minimum slab
> > + * alignment at runtime. The value returned by the function must be
> > + * >= ARCH_SLAB_MIN_MINALIGN.
> > + */
> > +#ifndef arch_slab_minalign
> > +static inline size_t arch_slab_minalign(void)
> > +{
> > + return ARCH_SLAB_MIN_MINALIGN;
> > +}
> > #endif
> >
> > /*
> > * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
> > - * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN
> > + * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN
> > * aligned pointers.
>
> This comment is not precise: kmalloc relies on kmem_cache_alloc, so
> kmalloc technically returns pointers aligned to
> max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MIN_MINALIGN). See
> create_kmalloc_cache()->create_boot_cache()->calculate_alignment() for
> SLAB and SLUB and __do_kmalloc_node() for SLOB. This alignment is
> stronger than the one is specified for __assume_kmalloc_alignment
> below, so the code should be fine. However, the comment is confusing.
>
> Also, the comment next to the ARCH_KMALLOC_MINALIGN definition says
> "Setting ARCH_KMALLOC_MINALIGN in arch headers" while it should say
> "Setting ARCH_DMA_MINALIGN in arch headers".
Good catches. Let's fix these issues separately (especially since I
reverted the ARCH_SLAB_MIN_MINALIGN change so the patches shouldn't
conflict). Would you like to send patches? I can if not.
Peter
On Fri, Apr 22, 2022 at 11:03 AM Catalin Marinas
<[email protected]> wrote:
>
> On Thu, Apr 21, 2022 at 02:15:48PM -0700, Peter Collingbourne wrote:
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 373b3ef99f4e..80e517593372 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object);
> > #endif
> >
> > /*
> > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
> > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment.
> > * Intended for arches that get misalignment faults even for 64 bit integer
> > * aligned buffers.
> > */
> > -#ifndef ARCH_SLAB_MINALIGN
> > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> > +#ifndef ARCH_SLAB_MIN_MINALIGN
> > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
> > +#endif
>
> Sorry, only a drive-by comment, I'll look at the arm64 parts next week.
> I've seen it mentioned in the first version, what's the point of MIN_MIN
> and not just MIN?
I tried to explain it here:
https://lore.kernel.org/all/CAMn1gO5xHZvFSSsW5sTVaUBN_gS-cYYNMG3PnpgCmh7kk_Zx7Q@mail.gmail.com/
In the end I decided to go back to MIN so this is moot.
Peter