iommu/amd: Use try_cmpxchg64() in v2_alloc_pte()

Use try_cmpxchg64() instead of cmpxchg64 (*ptr, old, new) != old in
v2_alloc_pte().  cmpxchg returns success in ZF flag, so this change
saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).

This is the same improvement as implemented for alloc_pte() in:

  commit 0d10fe7 ("iommu/amd: Use try_cmpxchg64 in alloc_pte and free_clear_pte")

Signed-off-by: Uros Bizjak <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Suravee Suthikulpanit <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Robin Murphy <[email protected]>
Reviewed-by: Vasant Hegde <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

Author: ubizjak

drivers/iommu/amd/io_pgtable_v2.c

@@ -158,7 +158,7 @@ static u64 *v2_alloc_pte(int nid, u64 *pgd, unsigned long iova,
 
 			__npte = set_pgtable_attr(page);
 			/* pte could have been changed somewhere. */
-			if (cmpxchg64(pte, __pte, __npte) != __pte)
+			if (!try_cmpxchg64(pte, &__pte, __npte))
 				iommu_free_page(page);
 			else if (IOMMU_PTE_PRESENT(__pte))
 				*updated = true;