Re: 5.1.0-rc1 regression: reset fails with kvm and -cpu host

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

+Vitaly

On 7/23/20 10:40 AM, Dr. David Alan Gilbert wrote:
> * Eduardo Habkost (ehabkost@redhat.com) wrote:
>> On Wed, Jul 22, 2020 at 04:47:32PM -0400, Eduardo Habkost wrote:
>>> On Wed, Jul 22, 2020 at 08:05:01PM +0200, Jan Kiszka wrote:
>>>> On 22.07.20 19:35, Eduardo Habkost wrote:
>>>>> Hi Jan,
>>>>>
>>>>> What was the last version where it worked for you?  Does using
>>>>> "-cpu host,-vmx" help?
>>>>
>>>> Yeah, -vmx does indeed help.
>>>>
>>>> I didn't have the time to bisect yet. Just check my reflog, picked
>>>> eb6490f544, and that works.
>>>
>>> Thanks!
>>>
>>> I could reproduce it locally[1], I will bisect it.
>>>
>>> The good news is that "-cpu host,+vmx" still works, on commit
>>> eb6490f544.
>>>
>>> [1] Linux 5.6.19-300.fc32.x86_64, Intel Core i7-8665U CPU.
>>
>> Bisected to:
>>
>> commit b16c0e20c74218f2d69710cedad11da7dd4d2190
>> Author: Paolo Bonzini <pbonzini@redhat.com>
>> Date:   Wed May 20 10:49:22 2020 -0400
>>
>>     KVM: add support for AMD nested live migration
>>
>>     Support for nested guest live migration is part of Linux 5.8, add the
>>     corresponding code to QEMU.  The migration format consists of a few
>>     flags, is an opaque 4k blob.
>>
>>     The blob is in VMCB format (the control area represents the L1 VMCB
>>     control fields, the save area represents the pre-vmentry state; KVM does
>>     not use the host save area since the AMD manual allows that) but QEMU
>>     does not really care about that.  However, the flags need to be
>>     copied to hflags/hflags2 and back.
>>
>>     In addition, support for retrieving and setting the AMD nested virtualization
>>     states allows the L1 guest to be reset while running a nested guest, but
>>     a small bug in CPU reset needs to be fixed for that to work.
>>
>>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> Guesswork led me to try reverting the chunk in kvm_put_nested_state;
> without it the reset seems to work; I can't explain that code though.
> 
> Dave
> 
>>
>> -- 
>> Eduardo
>>
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
>