linux-kernel - Re: [PATCH v2 4/5] iommu: Support mm PASID 1:n with sva domains

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Message-ID: <20b44fe8-33ba-d6ae-110e-a82a19390bcc@amd.com>
Date:   Thu, 31 Aug 2023 12:12:58 +0530
From:   Vasant Hegde <vasant.hegde@....com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Tina Zhang <tina.zhang@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Michael Shavit <mshavit@...gle.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] iommu: Support mm PASID 1:n with sva domains

On 8/31/2023 2:06 AM, Jason Gunthorpe wrote:
> On Mon, Aug 28, 2023 at 02:02:52PM +0530, Vasant Hegde wrote:
> 
>> I am not sure whether I understood the flow completely. Just wondering why you
>> are not freeing pasid in iommu_sva_unbind_device().
>> I mean once iommu_mm->sva_domains becomes free shouldn't we free the
>> iommu_mm->pasid?
> 
> No, for Intel use cases that PASID permanently becomes part of the
> ENQCMD MSR and cannot be revoked once it has been set
>  

Fair enough.

Patch description did explain it to some extent. ("The PASID is released in
__mmdrop()"). May be this needs to be expanded to cover why pasid is not
released in iommu_sva_unbind_device().


>> Also in this function (mm_pasid_drop()), should we check/free sva domains?
> 
> No, the driver must support a SVA domain with an empty mm_struct, eg
> by hooking release.

Sorry. Looks like confused you. Looking into code I got this.

My question was: when PASID is enabled, is there any chance of mm_pasid_drop()
getting called before freeing all SVA domains?

-Vasant