linux-kernel - [PATCH 2/2] iommu/vt-d: Remove caching mode check before devtlb flush

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Date: Sun,  7 Apr 2024 22:42:32 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: iommu@...ts.linux.dev
Cc: Kevin Tian <kevin.tian@...el.com>,
	Yi Liu <yi.l.liu@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	linux-kernel@...r.kernel.org,
	Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 2/2] iommu/vt-d: Remove caching mode check before devtlb flush

The Caching Mode (CM) of the Intel IOMMU indicates if the hardware
implementation caches not-present or erroneous translation-structure
entries except the first-stage translation. The caching mode is
unrelated to the device TLB , therefore there is no need to check
it before a device TLB invalidation operation.

Before the scalable mode is introduced, caching mode is treated as
an indication that the driver is running in a VM guest. This is just
a software contract as shadow page table is the only way to implement
a virtual IOMMU. But the VT-d spec doesn't state this anywhere. After
the scalable mode is introduced, this doesn't stand for anymore, as
caching mode is not relevant for the first-stage translation. A virtual
IOMMU implementation is free to support first-stage translation only
with caching mode cleared.

Remove the caching mode check before device TLB invalidation to ensure
compatibility with the scalable mode use cases.

Fixes: 792fb43ce2c9 ("iommu/vt-d: Enable Intel IOMMU scalable mode by default")
Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/intel/iommu.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 493b6a600394..681789b1258d 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1501,7 +1501,7 @@ static void iommu_flush_iotlb_psi(struct intel_iommu *iommu,
 	else
 		__iommu_flush_iotlb_psi(iommu, did, pfn, pages, ih);

-	if (!cap_caching_mode(iommu->cap) && !map)
+	if (!map)
 		iommu_flush_dev_iotlb(domain, addr, mask);
 }

@@ -1575,8 +1575,7 @@ static void intel_flush_iotlb_all(struct iommu_domain *domain)
 			iommu->flush.flush_iotlb(iommu, did, 0, 0,
 						 DMA_TLB_DSI_FLUSH);

-		if (!cap_caching_mode(iommu->cap))
-			iommu_flush_dev_iotlb(dmar_domain, 0, MAX_AGAW_PFN_WIDTH);
+		iommu_flush_dev_iotlb(dmar_domain, 0, MAX_AGAW_PFN_WIDTH);
 	}

 	if (dmar_domain->nested_parent)
-- 
2.34.1