[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

            Bug ID: 109456
           Summary: KVM VFIO guest X hang with guest kernel > 4.15
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: libgradev@gmail.com

Hi

Host: Arch running kernel 4.20.3 / Qemu 3.1
Guest: Ubuntu 18.04.1 (tried Ubuntu 18.10 also) with any kernel after 4.15
Driver: Happens with current stable, git from Padoka PPA and amdgpu-pro 18.50

Issue: Vega 64 passed through to guest causes X to hang on boot using 100% CPU
for one of the passed through cores for the Xorg process. X never starts with
the stopping point being 'LoadModule: "dri2"'. I cannot see any relevant errors
in Xorg.log or the KRB - though it's easily reproducible. The system is still
alive and can be ssh'd into.

Adding the nomodeset kernel option allows the guest to boot to GUI (albeit
without acceleration).

Details: With Qemu 3.0 having more than ~12GB RAM assigned to the guest causes
this behaviour. With Qemu 3.1 the amount of RAM is irrelevant - the hang always
occurs.

Believe this is related to one of the GPU reset patches added to the 4.16
kernel as the guest boots fine with Qemu 3.0/3.1 and guest kernel 4.15 (tested
up to 16GB guest RAM).

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #1 from Alex Deucher <alexdeucher@gmail.com> ---
Can you bisect?  Please attach your dmesg output and xorg log.

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #2 from libgradev@gmail.com ---
Created attachment 144034
  --> https://bugs.freedesktop.org/attachment.cgi?id=144034&action=edit
Git bisect log + result

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #3 from libgradev@gmail.com ---
Created attachment 144077
  --> https://bugs.freedesktop.org/attachment.cgi?id=144077&action=edit
Dmesg output from failed Xorg start

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #4 from libgradev@gmail.com ---
Created attachment 144078
  --> https://bugs.freedesktop.org/attachment.cgi?id=144078&action=edit
Xorg output from failed Xorg start

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #5 from libgradev@gmail.com ---
Have compiled 5.0.7 with the commit indicated by the bisect reverted and it
boots to Xorg fine.

Running an OpenGL application subsequently will hang the VM though.

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #6 from libgradev@gmail.com ---
Updated to QEMU 4.0.0 and re-tested - same result.

Let me know if you would like anything further info.

Thanks!

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #7 from Alex Williamson <alex.williamson@redhat.com> ---
Can you test this QEMU patch that's already in qemu.git for 4.1:

https://git.qemu.org/?p=qemu.git;a=commitdiff;h=3412d8ec9810b819f8b79e8e0c6b87217c876e32

Alternatively, setting the pci-hole64-size=0 can also avoid this issue:

 -global i440FX-pcihost.pci-hole64-size=0

or

 -global q35-host.pci-hole64-size=0

depending on your VM machine type.

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

--- Comment #8 from libgradev@gmail.com ---
Got back to this again recently and can confirm it's fixed in Qemu git (for
4.1) now.

Many thanks :)

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[Bug 109456] KVM VFIO guest X hang with guest kernel > 4.15

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https://bugs.freedesktop.org/show_bug.cgi?id=109456

libgradev@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

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