linux-kernel - [PATCH 1/3] iommu/amd: Use try_cmpxchg64() in v2_alloc

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Date: Wed, 22 May 2024 10:26:47 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Joerg Roedel <joro@...tes.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>
Subject: [PATCH 1/3] 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 0d10fe759117 ("iommu/amd: Use try_cmpxchg64 in alloc_pte and free_clear_pte")

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Joerg Roedel <joro@...tes.org>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Robin Murphy <robin.murphy@....com>
---
 drivers/iommu/amd/io_pgtable_v2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/io_pgtable_v2.c b/drivers/iommu/amd/io_pgtable_v2.c
index 78ac37c5ccc1..664e91c88748 100644
--- a/drivers/iommu/amd/io_pgtable_v2.c
+++ b/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;
-- 
2.45.1