path: root/arch/arm64/include/asm/pgtable.h
diff options
authorCatalin Marinas <catalin.marinas@arm.com>2016-04-13 16:01:22 +0100
committerWill Deacon <will.deacon@arm.com>2016-04-15 18:06:09 +0100
commit66dbd6e61a526ae7d11a208238ae2c17e5cacb6b (patch)
treeb9161efd6f9d4d40bb044c1e63b47ce4d70cd468 /arch/arm64/include/asm/pgtable.h
parentarm64, mm, numa: Add NUMA balancing support for arm64. (diff)
arm64: Implement ptep_set_access_flags() for hardware AF/DBM
When hardware updates of the access and dirty states are enabled, the default ptep_set_access_flags() implementation based on calling set_pte_at() directly is potentially racy. This triggers the "racy dirty state clearing" warning in set_pte_at() because an existing writable PTE is overridden with a clean entry. There are two main scenarios for this situation: 1. The CPU getting an access fault does not support hardware updates of the access/dirty flags. However, a different agent in the system (e.g. SMMU) can do this, therefore overriding a writable entry with a clean one could potentially lose the automatically updated dirty status 2. A more complex situation is possible when all CPUs support hardware AF/DBM: a) Initial state: shareable + writable vma and pte_none(pte) b) Read fault taken by two threads of the same process on different CPUs c) CPU0 takes the mmap_sem and proceeds to handling the fault. It eventually reaches do_set_pte() which sets a writable + clean pte. CPU0 releases the mmap_sem d) CPU1 acquires the mmap_sem and proceeds to handle_pte_fault(). The pte entry it reads is present, writable and clean and it continues to pte_mkyoung() e) CPU1 calls ptep_set_access_flags() If between (d) and (e) the hardware (another CPU) updates the dirty state (clears PTE_RDONLY), CPU1 will override the PTR_RDONLY bit marking the entry clean again. This patch implements an arm64-specific ptep_set_access_flags() function to perform an atomic update of the PTE flags. Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits") Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Reported-by: Ming Lei <tom.leiming@gmail.com> Tested-by: Julien Grall <julien.grall@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: <stable@vger.kernel.org> # 4.3+ [will: reworded comment] Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to '')
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 3c91b179089a..3eefc181d00b 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -535,6 +535,11 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
+extern int ptep_set_access_flags(struct vm_area_struct *vma,
+ unsigned long address, pte_t *ptep,
+ pte_t entry, int dirty);
* Atomic pte/pmd modifications.