From: Catalin Marinas <catalin.marinas@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org,
Will Deacon <will@kernel.org>,
Dave P Martin <Dave.Martin@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Peter Collingbourne <pcc@google.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH v5 10/25] arm64: mte: Tags-aware aware memcmp_pages() implementation
Date: Wed, 24 Jun 2020 18:52:29 +0100 [thread overview]
Message-ID: <20200624175244.25837-11-catalin.marinas@arm.com> (raw)
In-Reply-To: <20200624175244.25837-1-catalin.marinas@arm.com>
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>
---
Notes:
v4:
- Remove page tag comparison. This is not very useful to detect
identical pages as long as set_pte_at() can zero the tags on a page
without copy-on-write if mapped with PROT_MTE. This can be improved
if a real case appears but it's unlikely for heap pages to be
identical across multiple processes.
- Move the memcmp_pages() function to mte.c.
arch/arm64/kernel/mte.c | 26 ++++++++++++++++++++++++++
mm/util.c | 2 +-
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 5bf9bbed5a25..5f54fd140610 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -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())
diff --git a/mm/util.c b/mm/util.c
index c63c8e47be57..c856f5fec69d 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -911,7 +911,7 @@ 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;
next prev parent reply other threads:[~2020-06-24 17:53 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 17:52 [PATCH v5 00/25] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 01/25] arm64: mte: system register definitions Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 02/25] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 03/25] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 04/25] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 05/25] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 06/25] mm: Add PG_ARCH_2 page flag Catalin Marinas
2020-06-24 18:33 ` Andrew Morton
2020-06-24 18:36 ` Matthew Wilcox
2020-06-25 17:10 ` Catalin Marinas
2020-07-01 17:30 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 07/25] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 08/25] arm64: mte: Tags-aware copy_{user_,}highpage() implementations Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 09/25] arm64: Avoid unnecessary clear_user_page() indirection Catalin Marinas
2020-06-24 17:52 ` Catalin Marinas [this message]
2020-06-24 17:52 ` [PATCH v5 11/25] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-06-24 18:36 ` Andrew Morton
2020-06-25 17:34 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 12/25] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 13/25] mm: Introduce arch_validate_flags() Catalin Marinas
2020-06-24 18:37 ` Andrew Morton
2020-06-24 17:52 ` [PATCH v5 14/25] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 15/25] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-06-24 18:42 ` Andrew Morton
2020-06-24 17:52 ` [PATCH v5 16/25] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 17/25] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 18/25] arm64: mte: Restore the GCR_EL1 register after a suspend Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 19/25] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Catalin Marinas
2020-06-25 17:10 ` Luis Machado
2020-07-01 17:16 ` Catalin Marinas
2020-07-01 17:32 ` Luis Machado
2020-07-03 13:18 ` Catalin Marinas
2020-07-03 10:50 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 20/25] fs: Handle intra-page faults in copy_mount_options() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 21/25] mm: Add arch hooks for saving/restoring tags Catalin Marinas
2020-06-24 18:45 ` Andrew Morton
2020-06-25 9:04 ` Steven Price
2020-06-25 12:09 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 22/25] arm64: mte: Enable swap of tagged pages Catalin Marinas
2020-06-25 11:37 ` Steven Price
2020-06-25 11:59 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 23/25] arm64: mte: Save tags when hibernating Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 24/25] arm64: mte: Kconfig entry Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 25/25] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
2020-06-25 12:22 ` Szabolcs Nagy
2020-06-26 14:54 ` Catalin Marinas
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