From: Sean Christopherson <seanjc@google.com>
To: "Christian König" <christian.koenig@amd.com>,
"Dmitry Osipenko" <dmitry.osipenko@collabora.com>,
"David Airlie" <airlied@linux.ie>,
"Huang Rui" <ray.huang@amd.com>,
"Trigger Huang" <Trigger.Huang@gmail.com>,
"Gert Wollny" <gert.wollny@collabora.com>,
"Antonio Caggiano" <antonio.caggiano@collabora.com>,
dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
"Dmitry Osipenko" <digetx@gmail.com>,
kvm@vger.kernel.org, kernel@collabora.com,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v1] drm/ttm: Refcount allocated tail pages
Date: Wed, 11 Jan 2023 17:13:23 +0000 [thread overview]
Message-ID: <Y77uM/X94DtKXtK0@google.com> (raw)
In-Reply-To: <YxeoEr6xAtlZ+IrU@phenom.ffwll.local>
On Tue, Sep 06, 2022, Daniel Vetter wrote:
> On Tue, Sep 06, 2022 at 10:01:47PM +0200, Daniel Vetter wrote:
> > On Mon, Aug 15, 2022 at 12:05:19PM +0200, Christian König wrote:
> > > Am 15.08.22 um 11:54 schrieb Dmitry Osipenko:
> > > > Higher order pages allocated using alloc_pages() aren't refcounted and they
> > > > need to be refcounted, otherwise it's impossible to map them by KVM. This
> > > > patch sets the refcount of the tail pages and fixes the KVM memory mapping
> > > > faults.
> > > >
> > > > Without this change guest virgl driver can't map host buffers into guest
> > > > and can't provide OpenGL 4.5 profile support to the guest. The host
> > > > mappings are also needed for enabling the Venus driver using host GPU
> > > > drivers that are utilizing TTM.
> > > >
> > > > Based on a patch proposed by Trigger Huang.
> > >
> > > Well I can't count how often I have repeated this: This is an absolutely
> > > clear NAK!
> > >
> > > TTM pages are not reference counted in the first place and because of this
> > > giving them to virgl is illegal.
> > >
> > > Please immediately stop this completely broken approach. We have discussed
> > > this multiple times now.
> >
> > Yeah we need to get this stuff closed for real by tagging them all with
> > VM_IO or VM_PFNMAP asap.
>
> For a bit more context: Anything mapping a bo should be VM_SPECIAL. And I
> think we should add the checks to the gem and dma-buf mmap functions to
> validate for that, and fix all the fallout.
>
> Otherwise this dragon keeps resurrecting ...
>
> VM_SPECIAL _will_ block get_user_pages, which will block everyone from
> even trying to refcount this stuff.
FWIW, IIUC that won't change the KVM story. KVM acquires the PFN for these pages
via follow_pte(), not by gup(). Details are in a different strand of this thread[*].
If TTM pages aren't tied into mmu_notifiers, then I believe the only solution is
to not allow them to be mapped into user page tables. If they are tied into
mmu_notifiers, then this is fully a KVM limitation that we are (slowly) resolving.
[*] https://lore.kernel.org/all/Y77sQZI0IfFVx7Jo@google.com
next prev parent reply other threads:[~2023-01-11 17:13 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-15 9:54 [PATCH v1] drm/ttm: Refcount allocated tail pages Dmitry Osipenko
2022-08-15 10:05 ` Christian König
2022-08-15 10:09 ` Dmitry Osipenko
2022-08-15 10:11 ` Christian König
2022-08-15 10:14 ` Christian König
2022-08-15 10:18 ` Dmitry Osipenko
2022-08-15 10:42 ` Christian König
2022-08-15 10:47 ` Dmitry Osipenko
2022-08-15 10:51 ` Christian König
2022-08-15 11:19 ` Dmitry Osipenko
2022-08-15 11:28 ` Christian König
2022-08-15 11:50 ` Dmitry Osipenko
2022-08-15 13:06 ` Christian König
2022-08-15 13:45 ` Dmitry Osipenko
2022-08-15 13:53 ` Christian König
2022-08-15 14:57 ` Dmitry Osipenko
2022-08-15 15:54 ` Dmitry Osipenko
2022-08-17 22:57 ` Dmitry Osipenko
2022-08-17 23:13 ` Dmitry Osipenko
2022-08-18 9:41 ` Christian König
2023-01-11 17:05 ` Sean Christopherson
2023-01-11 21:24 ` Dmitry Osipenko
2022-09-06 20:01 ` Daniel Vetter
2022-09-06 20:05 ` Daniel Vetter
2022-09-07 6:48 ` Christian König
2023-01-11 17:13 ` Sean Christopherson [this message]
2022-09-08 11:04 ` Rob Clark
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