iommu/vt-d: Use try_cmpxchg64{,_local}() in iommu.c

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>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240414162454.49584-1-ubizjak@gmail.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index a7ecd90303dc42f9fbe120e75f2053b1390c5445..4a2afe89b464d191091e107c01de54e00c3f0a2e 100644 (file)
--- 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);