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arm64: mte: Tags-aware aware memcmp_pages() implementation

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When the Memory Tagging Extension is enabled, two pages are identical
only if both their data and tags are identical.

Make the generic memcmp_pages() a __weak function and add an
arm64-specific implementation which returns non-zero if any of the two
pages contain valid MTE tags (PG_mte_tagged set). There isn't much
benefit in comparing the tags of two pages since these are normally used
for heap allocations and likely to differ anyway.

Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
This commit is contained in:
Catalin Marinas 2019-11-27 09:53:44 +00:00
parent 738c8780fc
commit 4d1a8a2dc0
2 changed files with 27 additions and 1 deletions
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26
arch/arm64/kernel/mte.c
View File

@ -5,6 +5,7 @@
#include <linux/bitops.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/thread_info.h>
#include <asm/cpufeature.h>
@ -23,6 +24,31 @@ void mte_sync_tags(pte_t *ptep, pte_t pte)
}
}
int memcmp_pages(struct page *page1, struct page *page2)
{
char *addr1, *addr2;
int ret;
addr1 = page_address(page1);
addr2 = page_address(page2);
ret = memcmp(addr1, addr2, PAGE_SIZE);
if (!system_supports_mte() || ret)
return ret;
/*
* If the page content is identical but at least one of the pages is
* tagged, return non-zero to avoid KSM merging. If only one of the
* pages is tagged, set_pte_at() may zero or change the tags of the
* other page via mte_sync_tags().
*/
if (test_bit(PG_mte_tagged, &page1->flags) ||
test_bit(PG_mte_tagged, &page2->flags))
return addr1 != addr2;
return ret;
}
void flush_mte_state(void)
{
if (!system_supports_mte())

2
mm/util.c
View File

@ -957,7 +957,7 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
return res;
}
int memcmp_pages(struct page *page1, struct page *page2)
int __weak memcmp_pages(struct page *page1, struct page *page2)
{
char *addr1, *addr2;
int ret;