linux-kernel - Re: [PATCH v2 2/2] vfio/iommu_type1: Sanity check pfn_list when remove vfio

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Date:   Thu, 21 Jan 2021 11:14:14 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Keqian Zhu <zhukeqian1@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Will Deacon <will@...nel.org>, "Marc Zyngier" <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        "Robin Murphy" <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Suzuki K Poulose" <suzuki.poulose@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>
Subject: Re: [PATCH v2 2/2] vfio/iommu_type1: Sanity check pfn_list when
 remove vfio_dma

On Mon, 18 Jan 2021 21:16:08 +0800
Keqian Zhu <zhukeqian1@...wei.com> wrote:

> On 2021/1/16 3:14, Alex Williamson wrote:
> > On Fri, 15 Jan 2021 17:26:43 +0800
> > Keqian Zhu <zhukeqian1@...wei.com> wrote:
> >   
> >> vfio_sanity_check_pfn_list() is used to check whether pfn_list of
> >> vfio_dma is empty when remove the external domain, so it makes a
> >> wrong assumption that only external domain will add pfn to dma pfn_list.
> >>
> >> Now we apply this check when remove a specific vfio_dma and extract
> >> the notifier check just for external domain.  
> > 
> > The page pinning interface is gated by having a notifier registered for
> > unmaps, therefore non-external domains would also need to register a
> > notifier.  There's currently no other way to add entries to the
> > pfn_list.  So if we allow pinning for such domains, then it's wrong to
> > WARN_ON() when the notifier list is not-empty when removing an external
> > domain.  Long term we should probably extend page {un}pinning for the
> > caller to pass their notifier to be validated against the notifier list
> > rather than just allowing page pinning if *any* notifier is registered.
> > Thanks,  
> I was misled by the code comments. So when the commit a54eb55045ae is
> added, the only user of pin interface is mdev vendor driver, but now
> we also allow iommu backed group to use this interface to constraint
> dirty scope. Is vfio_iommu_unmap_unpin_all() a proper place to put
> this WARN()?

vfio_iommu_unmap_unpin_all() deals with removing vfio_dmas, it's
logically unrelated to whether any driver is registered to receive
unmap notifications.  Thanks,

Alex