On 09/09/20 10:49, Vitaly Kuznetsov wrote:
> Ingo Molnar <mingo@xxxxxxxxxx> writes:
>
>> * Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>>
>>> Merge commit 26d05b368a5c0 ("Merge branch 'kvm-async-pf-int' into HEAD")
>>> tried to adapt the new interrupt based async PF mechanism to the newly
>>> introduced IDTENTRY magic but unfortunately it missed the fact that
>>> DEFINE_IDTENTRY_SYSVEC() doesn't call ack_APIC_irq() on its own and
>>> all DEFINE_IDTENTRY_SYSVEC() users have to call it manually.
>>>
>>> As the result all multi-CPU KVM guest hang on boot when
>>> KVM_FEATURE_ASYNC_PF_INT is present. The breakage went unnoticed because no
>>> KVM userspace (e.g. QEMU) currently set it (and thus async PF mechanism
>>> is currently disabled) but we're about to change that.
>>>
>>> Fixes: 26d05b368a5c0 ("Merge branch 'kvm-async-pf-int' into HEAD")
>>> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>>
>> This also fixes a kvmtool regression, but interestingly it does not set
>> KVM_FEATURE_ASYNC_PF_INT either AFAICS:
>>
>> kepler:~/kvmtool.git> git grep KVM_FEATURE_ASYNC_PF_INT
>> kepler:~/kvmtool.git>
>
> My wild guess would be that kvmtool doesn't manually set any of the KVM
> PV features:
>
> [vitty@vitty kvmtool]$ git grep KVM_FEATURE_
> [vitty@vitty kvmtool]$
>
> it just blindly passes whatever it gets from KVM via
> KVM_GET_SUPPORTED_CPUID to KVM_SET_CPUID2 and KVM_FEATURE_ASYNC_PF_INT
> among other PV features is set there by default.
>
>>
>> kepler:~/kvmtool.git> grep url .git/config
>> url = https://git.kernel.org/pub/scm/linux/kernel/git/will/kvmtool.git
>>
>> So either I missed the flag-setting in the kvmtools.git source, or maybe
>> there's some other way to trigger this bug?
>>
>> Anyway, please handle this as a v5.9 regression:
>>
>> Tested-by: Ingo Molnar <mingo@xxxxxxxxxx>
>
> Thanks!
>
Queued, thanks.
Paolo
