From f532c57985b1a7d6b7e37e05506b46d413e5cca4 Mon Sep 17 00:00:00 2001 From: Lu Baolu Date: Wed, 5 Aug 2026 07:43:10 +0800 Subject: [PATCH] iommu/vt-d: Clear Present bit before tearing down copied context entry copied_context_tear_down() zeroes the 128-bit context entry with context_clear_entry() while the Present bit is still set, and only then issues the context-cache and IOTLB invalidations. This leaves a window in which hardware can fetch a torn entry, with some fields already zeroed while Present is still set, leading to unpredictable behaviour or spurious faults. While x86 provides strong write ordering, the compiler may reorder the writes to the two 64-bit halves of the entry, and the hardware fetch is not guaranteed to be atomic with respect to multiple CPU writes. There is no cacheline flush before the invalidation either, so on an IOMMU without coherent access to the context table the zeroed entry may not be visible to hardware at the point the invalidation is submitted. Apply the same ownership handshake described in the VT-d spec, Section 6.5.3.3 ("Guidance to Software for Invalidations"): clear only the Present bit, flush it out to the IOMMU, perform the invalidations, and only then zero the remainder of the entry. Fixes: c7191984e5aad ("iommu/vt-d: Factor out helpers from domain_context_mapping_one()") Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260602233426.357499-1-baolu.lu%40linux.intel.com Assisted-by: Claude:claude-opus-5 Signed-off-by: Lu Baolu Signed-off-by: Joerg Roedel --- drivers/iommu/intel/iommu.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 7098a6bf6a40..000b81cf4a7a 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -1109,7 +1109,8 @@ static void copied_context_tear_down(struct intel_iommu *iommu, assert_spin_locked(&iommu->lock); did_old = context_domain_id(context); - context_clear_entry(context); + context_clear_present(context); + __iommu_flush_cache(iommu, context, sizeof(*context)); if (did_old < iommu->max_domain_id) { iommu->flush.flush_context(iommu, did_old, @@ -1120,6 +1121,9 @@ static void copied_context_tear_down(struct intel_iommu *iommu, DMA_TLB_DSI_FLUSH); } + context_clear_entry(context); + __iommu_flush_cache(iommu, context, sizeof(*context)); + clear_context_copied(iommu, bus, devfn); }