linux-kernel - [PATCH 1/1] iommu: Avoid unnecessary cache invalidations

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Date:   Thu, 26 Oct 2023 16:49:42 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 1/1] iommu: Avoid unnecessary cache invalidations

The iommu_create_device_direct_mappings() only needs to flush the caches
when the mappings are changed in the affected domain. This is not true
for non-DMA domains, or for devices attached to the domain that have no
reserved regions. To avoid unnecessary cache invalidations, add a check
before iommu_flush_iotlb_all().

Fixes: a48ce36e2786 ("iommu: Prevent RESV_DIRECT devices from blocking domains")
Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 00d0a2b5d7dc..0cb676590bfa 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1114,7 +1114,8 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
 
 	}
 
-	iommu_flush_iotlb_all(domain);
+	if (!list_empty(&mappings) && iommu_is_dma_domain(domain))
+		iommu_flush_iotlb_all(domain);
 
 out:
 	iommu_put_resv_regions(dev, &mappings);
-- 
2.34.1