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

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Message-ID: <cdb6fb16-157e-059e-44ee-515fb4aca9af@linux.intel.com>
Date:   Thu, 7 Feb 2019 13:30:24 -0800
From:   sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>
Cc:     joro@...tes.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v1 1/1] iommu/vt-d: Enable PRI only if the device enables
 PASID.


On 2/7/19 1:15 PM, David Woodhouse wrote:
> On Thu, 2019-02-07 at 13:09 -0800, Raj, Ashok wrote:
>> You are right.. they are completely orthogonal. We just don't have
>> a way to handle the page-requests for request without PASID's.
>>
>> There are some of the vIOMMU work to pass the PRI to who owns
>> the device, and we can certainly relax it then. This is just to reflect
>> what support exists today. FWIW, even the native driver maybe be able
>> to resolve this if supported.
> As things stand, if a device makes a PRI request without a PASID, it'll
> get told that we didn't manage to bring the page in for it. Which is
> true.
>
> What's the actual problem being fixed by this patch?
Since the request is going to fail any way why go through the process of 
enabling it ? Once the functionality (PRI without PASID) is supported, 
then they can revert this patch. Just we are trying to expose whats 
currently supported clearly.
> Yes, we're going
> to want to hook up a way to pass the PRI to the right place... but why
> add *another* thing that's just going to have to be fixed, by reverting
> this patch?
>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer