linux-kernel - [PATCH 2/5] iommu/vt-d: Set SNP bit only in second-level page table entries

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Date:   Sun,  1 May 2022 19:24:31 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>
Cc:     Jacob jun Pan <jacob.jun.pan@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 2/5] iommu/vt-d: Set SNP bit only in second-level page table entries

The SNP bit is only valid for second-level PTEs. Setting this bit in the
first-level PTEs has no functional impact because the Intel IOMMU always
ignores the same bit in first-level PTEs. Anyway, let's check the page
table type before setting SNP bit in PTEs to make the code more readable.

Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/intel/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index d68f5bbf3e93..98050943d863 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4431,7 +4431,7 @@ static int intel_iommu_map(struct iommu_domain *domain,
 		prot |= DMA_PTE_READ;
 	if (iommu_prot & IOMMU_WRITE)
 		prot |= DMA_PTE_WRITE;
-	if (dmar_domain->force_snooping)
+	if (dmar_domain->force_snooping && !domain_use_first_level(dmar_domain))
 		prot |= DMA_PTE_SNP;
 
 	max_addr = iova + size;
-- 
2.25.1