linux-kernel - Re: [PATCH] iommu/amd: Fix IOMMU page flush when detach all devices from a domain

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Message-ID: <e27055c1-89b0-e804-b99c-c94965de5344@amd.com>
Date:   Tue, 22 Jan 2019 15:53:18 +0000
From:   "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
To:     "joro@...tes.org" <joro@...tes.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "Singh, Brijesh" <brijesh.singh@....com>
Subject: Re: [PATCH] iommu/amd: Fix IOMMU page flush when detach all devices
 from a domain

Joerg,

On 1/22/19 5:44 PM, joro@...tes.org wrote:
> Hi Suravee,
> 
> On Thu, Jan 17, 2019 at 08:44:36AM +0000, Suthikulpanit, Suravee wrote:
>> Then, in __domain_flush_pages, we issue command when the dev_iommu[] >= 0.
>> This should preserve previous behavior, and only add flushing condition to
>> the specific IOMMU in detached state. Please let me know what you think.
> 
> I think the whole point why VFIO is detaching all devices first and then
> goes into unmapping pages is that there are no flushes needed anymore
> when devices are detached.
> 
> But when we follow your proposal we would still do IOTLB flushes even
> when no devices are attached anymore. So I'd like to avoid this, given
> the implications on unmapping performance. We should just flush the
> IOMMU TLB at detach time and be done with it.
> 
> Makes sense?
> 
> Regards,
> 
> 	Joerg
> 

Thanks for the detail. Alright then, let's just go with the version you
sent on 1/16/19. Do you want me to resend V3 with that changes, or
would you be taking care of that?

Thanks,
Suravee