linux-kernel - [PATCH 1/1] iommu/vt-d: Remove commented-out code

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Date:   Fri,  9 Jun 2023 14:05:14 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     iommu@...ts.linux.dev
Cc:     linux-kernel@...r.kernel.org, Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 1/1] iommu/vt-d: Remove commented-out code

These lines of code were commented out when they were first added in commit
ba39592764ed ("Intel IOMMU: Intel IOMMU driver"). We do not want to restore
them because the VT-d spec has deprecated the read/write draining hit.

VT-d spec (section 11.4.2):
"
 Hardware implementation with Major Version 2 or higher (VER_REG), always
 performs required drain without software explicitly requesting a drain in
 IOTLB invalidation. This field is deprecated and hardware  will always
 report it as 1 to maintain backward compatibility with software.
"

Remove the code to make the code cleaner.

Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/intel/iommu.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 4c0b7424c45e..e5c111ff4dd9 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1312,15 +1312,7 @@ static void __iommu_flush_iotlb(struct intel_iommu *iommu, u16 did,
 			iommu->name, type);
 		return;
 	}
-	/* Note: set drain read/write */
-#if 0
-	/*
-	 * This is probably to be super secure.. Looks like we can
-	 * ignore it without any impact.
-	 */
-	if (cap_read_drain(iommu->cap))
-		val |= DMA_TLB_READ_DRAIN;
-#endif
+
 	if (cap_write_drain(iommu->cap))
 		val |= DMA_TLB_WRITE_DRAIN;

-- 
2.34.1