linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when TES=0

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Date:   Wed, 29 Nov 2023 16:10:20 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when
 TES=0

On Tue, Nov 14, 2023 at 09:10:34AM +0800, Lu Baolu wrote:
> The latest VT-d spec indicates that when remapping hardware is disabled
> (TES=0 in Global Status Register), upstream ATS Invalidation Completion
> requests are treated as UR (Unsupported Request).
> 
> Consequently, the spec recommends in section 4.3 Handling of Device-TLB
> Invalidations that software refrain from submitting any Device-TLB
> invalidation requests when address remapping hardware is disabled.
> 
> Verify address remapping hardware is enabled prior to submitting Device-
> TLB invalidation requests.
> 
> 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/dmar.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)

How did you get to the point where flush_dev_iotlb could even be
called if the iommu has somehow been globally disabled?

Shouldn't the attach of the domain compeltely fail if the HW is
disabled?

If the domain is not attached to anything why would flushing happen?

Jason