linux-kernel - [PATCH 1/5] iommu/vt-d: Restore WO permissions on second-level paging entries

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Message-ID: <20250513030739.2718555-2-baolu.lu@linux.intel.com>
Date: Tue, 13 May 2025 11:07:35 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: Joerg Roedel <joro@...tes.org>
Cc: iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/5] iommu/vt-d: Restore WO permissions on second-level paging entries

From: Jason Gunthorpe <jgg@...dia.com>

VT-D HW can do WO permissions on the second-stage but not the first-stage
page table formats. The commit eea53c581688 ("iommu/vt-d: Remove WO
permissions on second-level paging entries") wanted to make this uniform
for VT-D by disabling the support for WO permissions in the second-stage.

This isn't consistent with how other drivers are working. Instead if the
underlying HW can support WO, it should. For instance AMD already supports
WO on its second stage (v1) format and not its first (v2).

If WO support needs to be discoverable it should be done through an
iommu_domain capability flag.

Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Reviewed-by: Kevin Tian <kevin.tian@...el.com>
Link: https://lore.kernel.org/r/0-v1-c26553717e90+65f-iommu_vtd_ss_wo_jgg@nvidia.com
Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/intel/iommu.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index cb0b993bebb4..67c6ea1d8d44 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1681,9 +1681,8 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
 	}

 	attr = prot & (DMA_PTE_READ | DMA_PTE_WRITE | DMA_PTE_SNP);
-	attr |= DMA_FL_PTE_PRESENT;
 	if (domain->use_first_level) {
-		attr |= DMA_FL_PTE_US | DMA_FL_PTE_ACCESS;
+		attr |= DMA_FL_PTE_PRESENT | DMA_FL_PTE_US | DMA_FL_PTE_ACCESS;
 		if (prot & DMA_PTE_WRITE)
 			attr |= DMA_FL_PTE_DIRTY;
 	}
-- 
2.43.0