Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] iommu/amd: Use try_cmpxchg64 in alloc_pte and free_clear_pte | Date | Wed, 25 May 2022 16:54:16 +0200 |
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Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in alloc_pte and free_clear_pte. cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, remove racy explicit assignment to pteval when cmpxchg fails, this is what try_cmpxchg does implicitly from *pte in an atomic way.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Cc: Will Deacon <will@kernel.org> --- drivers/iommu/amd/io_pgtable.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/amd/io_pgtable.c b/drivers/iommu/amd/io_pgtable.c index 6608d1717574..7d4b61e5db47 100644 --- a/drivers/iommu/amd/io_pgtable.c +++ b/drivers/iommu/amd/io_pgtable.c @@ -258,7 +258,7 @@ static u64 *alloc_pte(struct protection_domain *domain, __npte = PM_LEVEL_PDE(level, iommu_virt_to_phys(page)); /* pte could have been changed somewhere. */ - if (cmpxchg64(pte, __pte, __npte) != __pte) + if (!try_cmpxchg64(pte, &__pte, __npte)) free_page((unsigned long)page); else if (IOMMU_PTE_PRESENT(__pte)) *updated = true; @@ -341,10 +341,8 @@ static void free_clear_pte(u64 *pte, u64 pteval, struct list_head *freelist) u64 *pt; int mode; - while (cmpxchg64(pte, pteval, 0) != pteval) { + while (!try_cmpxchg64(pte, &pteval, 0)) pr_warn("AMD-Vi: IOMMU pte changed since we read it\n"); - pteval = *pte; - } if (!IOMMU_PTE_PRESENT(pteval)) return; -- 2.35.3
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