linux-kernel - Re: [PATCH v3 1/1] iommu/vt-d: Remove caching mode check before device TLB flush

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Message-ID: <daf746ef-f5db-46aa-876f-42a9deb65445@linux.intel.com>
Date: Wed, 24 Apr 2024 11:41:05 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: iommu@...ts.linux.dev
Cc: baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.com>,
 Yi Liu <yi.l.liu@...el.com>, Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] iommu/vt-d: Remove caching mode check before
 device TLB flush

On 4/15/24 9:38 AM, Lu Baolu wrote:
> The Caching Mode (CM) of the Intel IOMMU indicates if the hardware
> implementation caches not-present or erroneous translation-structure
> entries except for the first-stage translation. The caching mode is
> irrelevant to the device TLB, therefore there is no need to check it
> before a device TLB invalidation operation.
> 
> Remove two caching mode checks before device TLB invalidation in the
> driver. The removal of these checks doesn't change the driver's behavior
> in critical map/unmap paths. Hence, there is no functionality or
> performance impact, especially since commit <29b32839725f> ("iommu/vt-d:
> Do not use flush-queue when caching-mode is on") has already disabled
> flush-queue for caching mode. Therefore, caching mode will never call
> intel_flush_iotlb_all().
> 
> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
> Reviewed-by: Kevin Tian<kevin.tian@...el.com>
> ---
>   drivers/iommu/intel/iommu.c | 9 ++-------
>   1 file changed, 2 insertions(+), 7 deletions(-)

Patch has been queued for iommu/vt-d.

Best regards,
baolu