[PATCH v3 39/62] iommu/amd: Document which IRTE fields amd_iommu_update_ga() can modify
From: Sean Christopherson <seanjc@google.com>
Date: 2025-06-11 22:48:03
Also in:
kvm, kvmarm, linux-iommu, lkml
Subsystem:
amd iommu (amd-vi), iommu subsystem, the rest · Maintainers:
Joerg Roedel, Will Deacon, Linus Torvalds
Add a comment to amd_iommu_update_ga() to document what fields it can safely modify without issuing an invalidation of the IRTE, and to explain its role in keeping GA IRTEs up-to-date. Per page 93 of the IOMMU spec dated Feb 2025: When virtual interrupts are enabled by setting MMIO Offset 0018h[GAEn] and IRTE[GuestMode=1], IRTE[IsRun], IRTE[Destination], and if present IRTE[GATag], are not cached by the IOMMU. Modifications to these fields do not require an invalidation of the Interrupt Remapping Table. Link: https://lore.kernel.org/all/9b7ceea3-8c47-4383-ad9c-1a9bbdc9044a@oracle.com (local) Cc: Joao Martins <redacted> Signed-off-by: Sean Christopherson <seanjc@google.com> --- drivers/iommu/amd/iommu.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 36749efcc781..5adc932b947e 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c@@ -3986,6 +3986,18 @@ int amd_iommu_create_irq_domain(struct amd_iommu *iommu) return 0; } +/* + * Update the pCPU information for an IRTE that is configured to post IRQs to + * a vCPU, without issuing an IOMMU invalidation for the IRTE. + * + * This API is intended to be used when a vCPU is scheduled in/out (or stops + * running for any reason), to do a fast update of IsRun and (conditionally) + * Destination. + * + * Per the IOMMU spec, the Destination, IsRun, and GATag fields are not cached + * and thus don't require an invalidation to ensure the IOMMU consumes fresh + * information. + */ int amd_iommu_update_ga(int cpu, bool is_run, void *data) { struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
--
2.50.0.rc1.591.g9c95f17f64-goog