linux-kernel - Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

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Message-ID: <YmgiQZZyFxsJ+9um@myrica>
Date:   Tue, 26 Apr 2022 17:48:01 +0100
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "zhangfei.gao@...mail.com" <zhangfei.gao@...mail.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, will@...nel.org,
        robin.murphy@....com, zhangfei.gao@...aro.org
Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit

On Tue, Apr 26, 2022 at 08:27:00AM -0700, Dave Hansen wrote:
> On 4/25/22 09:40, Jean-Philippe Brucker wrote:
> > The problem is that we'd have to request the device driver to stop DMA
> > before we can destroy the context and free the PASID. We did consider
> > doing this in the release() MMU notifier, but there were concerns about
> > blocking mmput() for too long (for example
> > https://lore.kernel.org/linux-iommu/4d68da96-0ad5-b412-5987-2f7a6aa796c3@amd.com/
> > though I think there was a more recent discussion). We also need to drain
> > the PRI and fault queues to get rid of all references to that PASID.
> 
> Is the concern truly about blocking mmput() itself?  Or, is it about
> releasing the resources associated with the mm?

The latter I think, this one was about releasing pages as fast as possible
if the process is picked by the OOM killer. 

Thanks,
Jean