Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] iommu/intel: Use try_cmpxchg64{,_local}() in iommu.c | Date | Sun, 14 Apr 2024 18:23:11 +0200 |
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Replace this pattern in iommu.c:
cmpxchg64{,_local}(*ptr, 0, new) != 0
.. with the simpler and faster:
!try_cmpxchg64{,_local}(*ptr, &tmp, new)
The x86 CMPXCHG instruction returns success in the ZF flag, so this change saves a compare after the CMPXCHG.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Lu Baolu <baolu.lu@linux.intel.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Will Deacon <will@kernel.org> Cc: Robin Murphy <robin.murphy@arm.com> --- drivers/iommu/intel/iommu.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 50eb9aed47cc..311073494f50 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -865,7 +865,7 @@ static struct dma_pte *pfn_to_dma_pte(struct dmar_domain *domain, break; if (!dma_pte_present(pte)) { - uint64_t pteval; + uint64_t pteval, tmp; tmp_page = alloc_pgtable_page(domain->nid, gfp); @@ -877,7 +877,8 @@ static struct dma_pte *pfn_to_dma_pte(struct dmar_domain *domain, if (domain->use_first_level) pteval |= DMA_FL_PTE_XD | DMA_FL_PTE_US | DMA_FL_PTE_ACCESS; - if (cmpxchg64(&pte->val, 0ULL, pteval)) + tmp = 0ULL; + if (!try_cmpxchg64(&pte->val, &tmp, pteval)) /* Someone else set it while we were thinking; use theirs. */ free_pgtable_page(tmp_page); else @@ -2128,8 +2129,8 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn, /* We don't need lock here, nobody else * touches the iova range */ - tmp = cmpxchg64_local(&pte->val, 0ULL, pteval); - if (tmp) { + tmp = 0ULL; + if (!try_cmpxchg64_local(&pte->val, &tmp, pteval)) { static int dumps = 5; pr_crit("ERROR: DMA PTE for vPFN 0x%lx already set (to %llx not %llx)\n", iov_pfn, tmp, (unsigned long long)pteval); -- 2.42.0
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