[PATCH 2/2] iommu/vt-d: Use WRITE_ONCE for setting root table entries

[Dmytro Maluka <dmaluka@chromium.org>]

Like context table entries in the previous patch, 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@chromium.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