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

[Eduardo Habkost <ehabkost@redhat.com>]

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>


-- 
Eduardo