linux-kernel - [PATCH v2] iommu/vt-d: Flush cache for PASID table before using it

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Message-ID: <20251221123508.37495-1-dmaluka@chromium.org>
Date: Sun, 21 Dec 2025 13:35:08 +0100
From: Dmytro Maluka <dmaluka@...omium.org>
To: David Woodhouse <dwmw2@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>,
	iommu@...ts.linux.dev
Cc: Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	linux-kernel@...r.kernel.org,
	"Vineeth Pillai (Google)" <vineeth@...byteword.org>,
	Aashish Sharma <aashish@...hishsharma.net>,
	Grzegorz Jaszczyk <jaszczyk@...omium.org>,
	Chuanxiao Dong <chuanxiao.dong@...el.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Dmytro Maluka <dmaluka@...omium.org>
Subject: [PATCH v2] iommu/vt-d: Flush cache for PASID table before using it

When writing the address of a freshly allocated zero-initialized PASID
table to a PASID directory entry, do that after the CPU cache flush for
this PASID table, not before it, to avoid the time window when this
PASID table may be already used by non-coherent IOMMU hardware while
its contents in RAM is still some random old data, not zero-initialized.

v1 -> v2:
Add Fixes: tag.

Fixes: 194b3348bdbb ("iommu/vt-d: Fix PASID directory pointer coherency")
Signed-off-by: Dmytro Maluka <dmaluka@...omium.org>
---
 drivers/iommu/intel/pasid.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index 3e2255057079..77b9b147ab50 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -153,6 +153,9 @@ static struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid)
 		if (!entries)
 			return NULL;
 
+		if (!ecap_coherent(info->iommu->ecap))
+			clflush_cache_range(entries, VTD_PAGE_SIZE);
+
 		/*
 		 * The pasid directory table entry won't be freed after
 		 * allocation. No worry about the race with free and
@@ -165,10 +168,8 @@ static struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid)
 			iommu_free_pages(entries);
 			goto retry;
 		}
-		if (!ecap_coherent(info->iommu->ecap)) {
-			clflush_cache_range(entries, VTD_PAGE_SIZE);
+		if (!ecap_coherent(info->iommu->ecap))
 			clflush_cache_range(&dir[dir_index].val, sizeof(*dir));
-		}
 	}
 
 	return &entries[index];
-- 
2.47.3