linux-kernel - [PATCH v2 5/5] iommu/vt-d: Use WRITE_ONCE for setting root table entries

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Message-ID: <20251227175728.4358-6-dmaluka@chromium.org>
Date: Sat, 27 Dec 2025 18:57:28 +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 5/5] iommu/vt-d: Use WRITE_ONCE for setting root table entries

Like context table entries (addressed in the previous patches), root
table entries may also be set up at runtime, when DMA translation is
already enabled (e.g. due to a device hotplug). So to stay on the safe
side, use WRITE_ONCE when setting a root table entry, to prevent the
compiler from doing store tearing which could result in setting the
present bit earlier than the context table address bits.

Signed-off-by: Dmytro Maluka <dmaluka@...omium.org>
---
 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 134302fbcd92..fe4d0d210a5f 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -374,7 +374,7 @@ struct context_entry *iommu_context_addr(struct intel_iommu *iommu, u8 bus,
 
 		__iommu_flush_cache(iommu, (void *)context, CONTEXT_SIZE);
 		phy_addr = virt_to_phys((void *)context);
-		*entry = phy_addr | 1;
+		WRITE_ONCE(*entry, phy_addr | 1);
 		__iommu_flush_cache(iommu, entry, sizeof(*entry));
 	}
 	return &context[devfn];
-- 
2.47.3