[libvirt] [Qemu-devel] [PULL v3 00/54] Kconfig conversion, excluding ARM and MIPS

[Laszlo Ersek]

Hi Paolo,

(+libvir-list)

I'd like to report a regression introduced by this patch set:

On 03/07/19 21:58, Paolo Bonzini wrote:
> The following changes since commit
> 6cb4f6db4f4367faa33da85b15f75bbbd2bed2a6:
>
>   Merge remote-tracking branch
>   'remotes/cleber/tags/python-next-pull-request' into staging
>   (2019-03-07 16:16:02 +0000)
>
> are available in the Git repository at:
>
>   git://github.com/bonzini/qemu.git tags/for-upstream-kconfig
>
> for you to fetch changes up to
> 576c3f2f16e7392e28cc9fe10d9a920d67d3645b:
>
>   kconfig: add documentation (2019-03-07 21:54:22 +0100)
>
> ----------------------------------------------------------------
> Initial Kconfig work, excluding ARM and MIPS
>
> ----------------------------------------------------------------

I use "libvirt-daemon-4.5.0-10.el7.x86_64" at the moment. Here are the
symptoms:

(1) the output of the following command changes across this series:

  virsh domcapabilities qemu /opt/qemu-installed-optimized/bin/qemu-system-aarch64 aarch64 virt-4.0

as shown by the diff

> @@ -92,6 +92,8 @@
>      <video supported='yes'>
>        <enum name='modelType'>
>          <value>vga</value>
> +        <value>cirrus</value>
> +        <value>vmvga</value>
>          <value>virtio</value>
>        </enum>
>      </video>
> @@ -111,10 +113,7 @@
>          <value>scsi</value>
>        </enum>
>        <enum name='capsType'/>
> -      <enum name='pciBackend'>
> -        <value>default</value>
> -        <value>vfio</value>
> -      </enum>
> +      <enum name='pciBackend'/>
>      </hostdev>
>    </devices>
>    <features>

(2) given the following domain XML snippet, in a qemu (not KVM) aarch64
guest that I have,

>     <video>
>       <model type='virtio' heads='1' primary='yes'/>
>       <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
>     </video>

the QEMU command line generated by libvirt changes:

> -  -device virtio-gpu-pci,id=video0,max_outputs=1,bus=pci.4,addr=0x0 \
> +  -device virtio-vga,id=video0,max_outputs=1,bus=pci.4,addr=0x0 \

Perhaps this series causes (1), which in turn causes (2), or else this
series causes both (1) and (2) independently of each other. I'm not sure
about that. Either way, (2) is a problem, because virtio-vga is
inappropriate for aarch64 guests (and the ArmVirtQemu platform firmware
in edk2 won't even try to drive it -- a blank screen is the result).


Now, I can't pinpoint an exact commit, because (after a *brutal*
bisection) I get:

> There are only 'skip'ped commits left to test.
> The first bad commit could be any of:
> a02c0edb35662de38d400f42b68845540669ca3d
> 03b348bdcbd1eda4ce097b2b84527dec774d80c4
> d6e9c470fc91f75db1785f17a9d3567d5a27953d
> a7e23159074c9d774fb1e88357b778994a0c9365
> bcb129b3154ba743f8e52c21c331a0dfcaee7c38
> 02017ee385ef574133c4a978d368640772978178
> 7c28b925b7e176b4e44ed05d23cf883561000546
> 1550b0e6bfe3ab6985e5ad75df1c528a0ca39468
> e9947d18df97e6c6584f020cf9cc995404cc8061
> 8f01b41e1098d8cb9491fa3ea7bd59cf187a5bd7
> 9533dcdd416530a0d72140c122bf90517b6c81eb
> 32690c8bed5762518272876dcb6dd39a54f54fd1
> c3a98aa54c734dcb7a36d193c6330d8f04d4bf8e
> ccf222a816d59af1318a7efb59c6b9c5578d1abf
> f349474920d80838ecea3d421531fdb0660b8740
> 2ac041c2c3d89691cda1657981c41fe4bc20244b
> e0e312f3525ad6ac18ba6633af29190dd9620cbc
> b42075bb77672616127c9452c0f836e757e9ce1a
> We cannot bisect more!

Here's how I built each step of the bisection:

- "git clean -ffdx" and "git submodule deinit --all --force" on the
  source directory

- create a new, pristine build directory

- configure QEMU for out-of-tree build, in that directory

- select the i386, x86_64, arm, and aarch64 targets (all softmmu)

- report "skip" to git-bisect iff the build breaks, otherwise test the
  aarch64 emulator through libvirt, and report good/bad dependent on the
  test result.

The bisection log is attached -- "git bisect replay" and "git bisect
visualize" should tell the story better than the above dump of commit
hashes. Basically:

- The tree builds up to and including commit 82f5181777eb ("kconfig:
  introduce kconfig files", 2019-03-07), and that commit works fine as
  well.

- Then the build breaks (starting with commit e0e312f3525a, "build:
  switch to Kconfig", 2019-03-07).

- The tree becomes buildable again at commit b42075bb7767 ("virtio:
  express virtio dependencies with Kconfig", 2019-03-07), but at that
  point, the functionality has been regressed.

Thanks,
Laszlo
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