From 66dbd6e61a526ae7d11a208238ae2c17e5cacb6b Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 13 Apr 2016 16:01:22 +0100 Subject: 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 Reported-by: Ming Lei Tested-by: Julien Grall Cc: Will Deacon Cc: # 4.3+ [will: reworded comment] Signed-off-by: Will Deacon --- arch/arm64/include/asm/pgtable.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/arm64/include') diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 3c91b17..3eefc18 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) } #ifdef CONFIG_ARM64_HW_AFDBM +#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS +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. */ -- cgit v1.1