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Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap
From: |
Aviv B.D. |
Subject: |
Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications |
Date: |
Mon, 21 Nov 2016 13:36:21 +0200 |
On Wed, Nov 16, 2016 at 9:57 PM, Michael S. Tsirkin <address@hidden> wrote:
> On Wed, Nov 16, 2016 at 09:50:46PM +0200, Aviv B.D. wrote:
> >
> >
> > On Wed, Nov 16, 2016 at 5:34 PM, Alex Williamson <
> address@hidden>
> > wrote:
> >
> > On Wed, 16 Nov 2016 15:54:56 +0200
> > "Michael S. Tsirkin" <address@hidden> wrote:
> >
> > > On Thu, Nov 10, 2016 at 12:44:47PM -0700, Alex Williamson wrote:
> > > > On Thu, 10 Nov 2016 21:20:36 +0200
> > > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > >
> > > > > On Thu, Nov 10, 2016 at 09:04:13AM -0700, Alex Williamson
> wrote:
> > > > > > On Thu, 10 Nov 2016 17:54:35 +0200
> > > > > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > > > >
> > > > > > > On Thu, Nov 10, 2016 at 08:30:21AM -0700, Alex Williamson
> wrote:
> > > > > > > > On Thu, 10 Nov 2016 17:14:24 +0200
> > > > > > > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > > > > > >
> > > > > > > > > On Tue, Nov 08, 2016 at 01:04:21PM +0200, Aviv B.D
> wrote:
> > > > > > > > > > From: "Aviv Ben-David" <address@hidden>
> > > > > > > > > >
> > > > > > > > > > * Advertize Cache Mode capability in iommu cap
> register.
> > > > > > > > > > This capability is controlled by "cache-mode"
> property of
> > intel-iommu device.
> > > > > > > > > > To enable this option call QEMU with "-device
> > intel-iommu,cache-mode=true".
> > > > > > > > > >
> > > > > > > > > > * On page cache invalidation in intel vIOMMU, check
> if the
> > domain belong to
> > > > > > > > > > registered notifier, and notify accordingly.
> > > > > > > > >
> > > > > > > > > This looks sane I think. Alex, care to comment?
> > > > > > > > > Merging will have to wait until after the release.
> > > > > > > > > Pls remember to re-test and re-ping then.
> > > > > > > >
> > > > > > > > I don't think it's suitable for upstream until there's a
> > reasonable
> > > > > > > > replay mechanism
> > > > > > >
> > > > > > > Could you pls clarify what do you mean by replay?
> > > > > > > Is this when you attach a device by hotplug to
> > > > > > > a running system?
> > > > > > >
> > > > > > > If yes this can maybe be addressed by disabling hotplug
> > temporarily.
> > > > > >
> > > > > > No, hotplug is not required, moving a device between existing
> > domains
> > > > > > requires replay, ie. actually using it for nested device
> > assignment.
> > > > >
> > > > > Good point, that one is a correctness thing. Aviv,
> > > > > could you add this in TODO list in a cover letter pls?
> > > > >
> > > > > > > > and we straighten out whether it's expected to get
> > > > > > > > multiple notifies and the notif-ee is responsible for
> filtering
> > > > > > > > them or if the notif-er should do filtering.
> > > > > > >
> > > > > > > OK this is a documentation thing.
> > > > > >
> > > > > > Well no, it needs to be decided and if necessary implemented.
> > > > >
> > > > > Let's assume it's the notif-ee for now. Less is more and all
> that.
> > > >
> > > > I think this is opposite of the approach dwg suggested.
> > > >
> > > > > > > > Without those, this is
> > > > > > > > effectively just an RFC.
> > > > > > >
> > > > > > > It's infrastructure without users so it doesn't break
> things,
> > > > > > > I'm more interested in seeing whether it's broken in
> > > > > > > some way than whether it's complete.
> > > > > >
> > > > > > If it allows use with vfio but doesn't fully implement the
> complete
> > set
> > > > > > of interfaces, it does break things. We currently prevent
> viommu
> > usage
> > > > > > with vfio because it is incomplete.
> > > > >
> > > > > Right - that bit is still in as far as I can see.
> > > >
> > > > Nope, 3/3 changes vtd_iommu_notify_flag_changed() to allow use
> with
> > > > vfio even though it's still incomplete. We would at least need
> > > > something like a replay callback for VT-d that triggers an abort
> if you
> > > > still want to accept it incomplete. Thanks,
> > > >
> > > > Alex
> > >
> > > IIUC practically things seems to work, right?
> >
> > AFAIK, no.
> >
> > > So how about disabling by default with a flag for people that want
> to
> > > experiment with it?
> > > E.g. x-vfio-allow-broken-translations ?
> >
> > We've already been through one round of "intel-iommu is incomplete
> for
> > use with device assignment, how can we prevent it from being used",
> > which led to the notify_flag_changed callback on
> MemoryRegionIOMMUOps.
> > This series now claims to fix that yet still doesn't provide a
> > mechanism to do memory_region_iommu_replay() given that VT-d has a
> much
> > larger address width. Why is the onus on vfio to resolve this or
> > provide some sort of workaround? vfio is using the QEMU iommu
> > interface correctly, intel-iommu is still incomplete. The least it
> > could do is add an optional replay callback to MemoryRegionIOMMUOps
> > that supersedes the existing memory_region_iommu_replay() code and
> > triggers an abort when it gets called. I don't know what an
> > x-vfio-allow-broken-translations option would do, how I'd implement
> it,
> > or why I'd bother to implement it. Thanks,
> >
> > Alex
> >
> >
> > I'll implement your suggestion regarding the replay framwork.
> > Probably in another patch set, if it is OK?
> >
> > Thanks,
> > Aviv.
> >
>
> Alex points out that with 3/3 setting cache_mode=1 will enable VFIO
> device assignment. Question would be, does it actually work for you
> in this mode? If not it seems important not to enable it for users.
>
> --
> MST
>
The patch is actually working with just commenting out the replay call in
vfio.
I didn't tested it with nesting environment but with DPDK it worked great.
Aviv.
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, (continued)
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/16
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/11/16
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Aviv B.D., 2016/11/16
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/16
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications,
Aviv B.D. <=
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/11/16
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/16
- Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Aviv B.D., 2016/11/16