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mm: make minimum slab alignment a runtime property 

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

[akpm@linux-foundation.org: make slab alignment type `unsigned int' to avoid casting]
Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead
Link: https://lkml.kernel.org/r/20220427195820.1716975-2-pcc@google.com
Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Peter Collingbourne 2022-05-09 18:20:53 -07:00 committed by Andrew Morton
parent 534aa1dc97
commit d949a8155d
5 changed files with 40 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
arch/arm64/include/asm/cache.h
View File

@ -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_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
#elif defined(CONFIG_KASAN_HW_TAGS)
static inline unsigned int 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

12
include/linux/slab.h
View File

@ -209,6 +209,18 @@ void kmem_dump_obj(void *object);
#define ARCH_SLAB_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 a power
* of two and >= ARCH_SLAB_MINALIGN.
*/
#ifndef arch_slab_minalign
static inline unsigned int arch_slab_minalign(void)
{
return ARCH_SLAB_MINALIGN;
}
#endif
/*
* kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
* pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN

7
mm/slab.c
View File

@ -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()=%u\n", objp,
arch_slab_minalign());
}
return objp;
}

3
mm/slab_common.c
View File

@ -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(align, arch_slab_minalign());
return ALIGN(align, sizeof(void *));
}

16
mm/slob.c
View File

@ -478,9 +478,11 @@ 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);
unsigned int minalign;
void *ret;
minalign = max_t(unsigned int, ARCH_KMALLOC_MINALIGN,
arch_slab_minalign());
gfp &= gfp_allowed_mask;
might_alloc(gfp);
@ -493,7 +495,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
* kmalloc()'d objects.
*/
if (is_power_of_2(size))
align = max(minalign, (int) size);
align = max_t(unsigned int, minalign, size);
if (!size)
return ZERO_SIZE_PTR;
@ -555,8 +557,11 @@ 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);
unsigned int align = max_t(unsigned int,
ARCH_KMALLOC_MINALIGN,
arch_slab_minalign());
unsigned int *m = (unsigned int *)(block - align);
slob_free(m, *m + align);
} else {
unsigned int order = folio_order(sp);
@ -573,7 +578,7 @@ EXPORT_SYMBOL(kfree);
size_t __ksize(const void *block)
{
struct folio *folio;
int align;
unsigned int align;
unsigned int *m;
BUG_ON(!block);
@ -584,7 +589,8 @@ 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(unsigned int, ARCH_KMALLOC_MINALIGN,
arch_slab_minalign());
m = (unsigned int *)(block - align);
return SLOB_UNITS(*m) * SLOB_UNIT;
}