[RFC PATCH] tests/qemuxml2*/graphics-spice-timeout: skip CPU model check

[Peter Krempa]

On Tue, Nov 16, 2021 at 21:11:50 -0300, Daniel Henrique Barboza wrote:
> Commit 65b0b746b516 changed spice tests to use latest caps. Before this
> change, "FLAG_REAL_CAPS" wasn't being set in testQemuInfoInitArgs(). The
> absence of this flag triggered the code path inside
> testCompareXMLToArgv() that executed testUpdateQEMUCaps(). This function
> will update the host CPU via virQEMUCapsUpdateHostCPUModel() into
> virQEMUCapsInitHostCPUModel().  In this function,
> virQEMUCapsInitCPUModel() would end up updating the hostCPU inside the
> qemuCaps (via virQEMUCapsProbeHostCPU()). Before the forementioned
> commit, the host CPU was being defaulted to x86_64, vendor Intel, for
> the 'graphics-spice-timeout' test that is using the 'pc' machine type
> and 'accel=kvm'.
> 
> Today, "FLAG_REAL_CAPS" is being set because we're using the latest caps
> from x86_64. This means that the whole code path mentioned above is
> skipped. qemuCaps are now being loaded via virQEMUCapsLoadCache()
> directly.  Without the handling being done by testUpdateQEMUCaps(), the
> host CPU is being retrieved later on, down below
> qemuProcessCreatePretendCmdPrepare() into qemuProcessUpdateGuestCPU().
> The latter will attempt to update the domain cpu and executing a
> virCPUCompare with the hostCPU and def->cpu.
> 
> All this logic ended up causing a failure of the
> 'graphics-spice-timeout' test in ppc64 and s390x hosts. This test is
> being run with KVM acceleration, and the KVM driver for ppc64 and s390x
> will return a default x86_64 CPU with vendor "AMD", making
> virCPUCompare() fail with the following message:

With all of this description which sounds plausible and pointing to the
root cause of tests not being stable enough when used with real caps,
the fix you are proposing seems to really just fix the symptom.

This patch itself is acceptable as is, but doesn't really fix the real
issue. If you don't plan on addressing the root cause, please:

1) note in the commit message for this commit that it's not really
   fixing the root cause, just the symptom

2) file an upstream issue with your analysis so that we don't forget
   that this is still broken

> "QEMU XML-2-ARGV graphics-spice-timeout.x86_64-latest   ... libvirt: CPU
> Driver error : the CPU is incompatible with host CPU: host CPU vendor does
> not match required CPU vendor Intel"
> 
> Fix this test by setting cpu check='none' and avoid the virCPUCompare()
> that causes the problem for ppc64 and s390x hosts.

To resolve point 1), be more explicit that it's just a symptom fix in
this sentence.

> 
> Reported-by: Boris Fiuczynski <fiuczy at linux.ibm.com>
> Signed-off-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> ---
> 
> Sending as a RFC because I'm not sure if this patch fixes the
> problem for s390x. Boris, can you please test and see if this
> fix works for you?

It is plausible it will work, there are other cases which use
match='exact' check='none' using real caps on X86 and they don't seem to
be causing problems.