linux-kernel - RE: [PATCH 1/2] iommu/vt-d: Avoid unnecessary device TLB flush in map path

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Date: Tue, 9 Apr 2024 07:21:34 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>
CC: "Liu, Yi L" <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" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] iommu/vt-d: Avoid unnecessary device TLB flush in map
 path

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Sunday, April 7, 2024 10:43 PM
> 
> iommu_flush_iotlb_psi() is called in map and unmap paths. The caching
> mode check before device TLB invalidation will cause device TLB
> invalidation always issued if IOMMU is not running in the caching mode.
> This is inefficient and causes performance overhead.
> 
> Make device TLB invalidation behavior consistent between batched mode
> unmapping and strict mode unmapping. Device TLB invalidation should only
> be requested in the unmap path if the IOMMU is not in caching mode.
> 
> Fixes: bf92df30df90 ("intel-iommu: Only avoid flushing device IOTLB for
> domain ID 0 in caching mode")
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

and given it only affects performance then not qualified for backporting?