linux-kernel - Re: [PATCH 1/1] iommu: Bind process address spaces to devices

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Message-ID: <20190228140950.GD1594@8bytes.org>
Date:   Thu, 28 Feb 2019 15:09:50 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        christian.koenig@....com, kevin.tian@...el.com,
        ashok.raj@...el.com, baolu.lu@...ux.intel.com,
        alex.williamson@...hat.com
Subject: Re: [PATCH 1/1] iommu: Bind process address spaces to devices

Hi Jacob,

On Wed, Feb 27, 2019 at 01:41:29PM -0800, Jacob Pan wrote:
> On Tue, 26 Feb 2019 12:17:43 +0100
> Joerg Roedel <joro@...tes.org> wrote:

> Just trying to understand how to use this API.
> So if we bind the same mm to two different devices, we should get two
> different iommu_sva handle, right?
> I think intel-svm still needs a flag argument for supervisor pasid etc.
> Other than that, I think both interface should work for vt-d.

I second Jean's question here, is supervisor pasid still needed with
scalable mode? What is the use-case and which mm_struct will be used for
supervisor accesses?

> Another question is that for nested SVA, we will need to bind guest mm.
> Do you think we should try to reuse this or have it separate? I am
> working on a separate API for now.

I think a separate API makes more sense. It could be somehow fit into
this as well, but having it separate is cleaner. And we already have
separate API for aux-domains, so this would be just another extension of
the IOMMU-API for using PASIDs.


> > 	int iommu_sva_get_pasid(struct iommu_sva *handle);
> If multiple bind to the same mm gets multiple handles, this API should
> retrieve the same pasid for different handle?

It can return the same handle if we store the pasid in the mm_struct,
for example ...
> Just curious why making the handle private instead of returning the
> pasid value in the handle?

... which is also the reason why I prefer the accessor function, it
allows to have the pasid not in the iommu_sva handle, but to retrieve it
from somewhere else (like the mm_struct).

Regards,

	Joerg