[PATCH] iommu/intel: Use try_cmpxchg64{,_local}() in iommu.c

Uros Bizjak
2024-04-14T16:25:07Z

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