linux-kernel - Re: [PATCH v1 1/1] iommu/vt-d: Enable PRI only if the device enables PASID.

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Date:   Thu, 07 Feb 2019 20:08:06 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com, joro@...tes.org
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v1 1/1] iommu/vt-d: Enable PRI only if the device
 enables PASID.

On Thu, 2019-02-07 at 10:44 -0800, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> Intel IOMMU Page Request Services (PRS) only works with devices which
> supports/uses PASID. So enable PRI only if the device also enables
> PASID support. For more details, Please check the implementation of PRQ
> handler(prq_event_thread()) in intel-svm driver.
> 
> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Cc: Ashok Raj <ashok.raj@...el.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

Hm, that shouldn't be true. PRI and PASID support are orthogonal.

If we get a PRI request without PASID, we should currently report it as
non-serviced which is the right thing to do. We can hook this up to KVM
etc. to actually allow paging of guests with devices attached, *if* the
devices attached to those guests support PRI.

Nothing fundamentally stops us using PRI without PASID support.



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