[RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[Hector Cao]

Hello,

Since it is a blocking issue for us, we went further and ended up with a solution along [1]
that allows us to get out of this situation.

The idea is to add compatibility properties to restore legacy behaviors for machine types
with older versions of QEMU (<10.1). 2 compatiblity properties have been added to address
respectively the 2 missing features, each one is done in a separate patch.

We know that 10.1 has been released and it's final, but working on a solution towards 11.0
would allow everyone to settle on the fix and even consider backporting where not yet released
like Ubuntu 25.10 for us.

It is important to have upstream support going forward in this or any other way
and therefore reach out with this RFC to ask you to think about it with us.

[1] https://gitlab.com/qemu-project/qemu/-/blob/master/docs/devel/migration/compatibility.rst

Hector Cao (2):
  target/i386: add compatibility property for arch_capabilities
  target/i386: add compatibility property for pdcm feature

 hw/core/machine.c     |  2 ++
 migration/migration.h | 23 +++++++++++++++++++++++
 migration/options.c   |  6 ++++++
 target/i386/cpu.c     | 17 ++++++++++++++---
 target/i386/kvm/kvm.c |  5 ++++-
 5 files changed, 49 insertions(+), 4 deletions(-)

-- 
2.45.2

[RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[Hector Cao]

[-- Attachment #1: Type: text/plain, Size: 230 bytes --]

Thanks Fiona Ebner for pointing out (in DM) that I did not CC to the
relevant maintainers.
Let me CC to maintainers that are listed by  the ./scripts/get_maintainer.pl
script on the submission changed files.

Kind regards,
Hector

[-- Attachment #2: Type: text/html, Size: 513 bytes --]

Re: [RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[Paolo Bonzini]

On 9/10/25 13:57, Hector Cao wrote:
> Hello,
> 
> Since it is a blocking issue for us, we went further and ended up with a solution along [1]
> that allows us to get out of this situation.
> 
> The idea is to add compatibility properties to restore legacy behaviors for machine types
> with older versions of QEMU (<10.1). 2 compatiblity properties have been added to address
> respectively the 2 missing features, each one is done in a separate patch.
> 
> We know that 10.1 has been released and it's final, but working on a solution towards 11.0
> would allow everyone to settle on the fix and even consider backporting where not yet released
> like Ubuntu 25.10 for us.

Thanks, I have applied the patch.  It's better to have the fix in 10.1.1.

Sorry for the delay, I was on vacation for one week and working reduced 
hours the next.

Paolo

> It is important to have upstream support going forward in this or any other way
> and therefore reach out with this RFC to ask you to think about it with us.
> 
> [1] https://gitlab.com/qemu-project/qemu/-/blob/master/docs/devel/migration/compatibility.rst
> 
> Hector Cao (2):
>    target/i386: add compatibility property for arch_capabilities
>    target/i386: add compatibility property for pdcm feature
> 
>   hw/core/machine.c     |  2 ++
>   migration/migration.h | 23 +++++++++++++++++++++++
>   migration/options.c   |  6 ++++++
>   target/i386/cpu.c     | 17 ++++++++++++++---
>   target/i386/kvm/kvm.c |  5 ++++-
>   5 files changed, 49 insertions(+), 4 deletions(-)
> 

Re: [RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[Hector Cao]

[-- Attachment #1: Type: text/plain, Size: 2029 bytes --]

Thanks Paolo,

Is it still time for me to submit the v2 of this patch ? I would like do
add 2 changes:
- add fixes:xxx line suggested by Daniel
- fix link error for qemu-user build (since it has no access to migration
code)

Best,
Hector

<https://launchpad.net/~hectorcao>

Le mar. 23 sept. 2025, 09:53, Paolo Bonzini <pbonzini@redhat.com> a écrit :

> On 9/10/25 13:57, Hector Cao wrote:
> > Hello,
> >
> > Since it is a blocking issue for us, we went further and ended up with a
> solution along [1]
> > that allows us to get out of this situation.
> >
> > The idea is to add compatibility properties to restore legacy behaviors
> for machine types
> > with older versions of QEMU (<10.1). 2 compatiblity properties have been
> added to address
> > respectively the 2 missing features, each one is done in a separate
> patch.
> >
> > We know that 10.1 has been released and it's final, but working on a
> solution towards 11.0
> > would allow everyone to settle on the fix and even consider backporting
> where not yet released
> > like Ubuntu 25.10 for us.
>
> Thanks, I have applied the patch.  It's better to have the fix in 10.1.1.
>
> Sorry for the delay, I was on vacation for one week and working reduced
> hours the next.
>
> Paolo
>
> > It is important to have upstream support going forward in this or any
> other way
> > and therefore reach out with this RFC to ask you to think about it with
> us.
> >
> > [1]
> https://gitlab.com/qemu-project/qemu/-/blob/master/docs/devel/migration/compatibility.rst
> >
> > Hector Cao (2):
> >    target/i386: add compatibility property for arch_capabilities
> >    target/i386: add compatibility property for pdcm feature
> >
> >   hw/core/machine.c     |  2 ++
> >   migration/migration.h | 23 +++++++++++++++++++++++
> >   migration/options.c   |  6 ++++++
> >   target/i386/cpu.c     | 17 ++++++++++++++---
> >   target/i386/kvm/kvm.c |  5 ++++-
> >   5 files changed, 49 insertions(+), 4 deletions(-)
> >
>
>

[-- Attachment #2: Type: text/html, Size: 3127 bytes --]

Re: [RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[Paolo Bonzini]

On Tue, Sep 23, 2025 at 12:08 PM Hector Cao <hector.cao@canonical.com> wrote:
>
> Thanks Paolo,
>
> Is it still time for me to submit the v2 of this patch ? I would like do add 2 changes:
> - add fixes:xxx line suggested by Daniel
> - fix link error for qemu-user build (since it has no access to migration code)

I have since noticed the link error indeed, and I'll post a v2 myself
with the fix.

Next time, if you notice a problem with the patch you should post the
fixed version without waiting for input.

Paolo

Re: [RFC PATCH 0/2] Fix cross migration issue with missing features: pdcm, arch-capabilities

[Hector Cao]

[-- Attachment #1: Type: text/plain, Size: 736 bytes --]

<https://launchpad.net/~hectorcao>

Le mar. 23 sept. 2025, 12:15, Paolo Bonzini <pbonzini@redhat.com> a écrit :

> On Tue, Sep 23, 2025 at 12:08 PM Hector Cao <hector.cao@canonical.com>
> wrote:
> >
> > Thanks Paolo,
> >
> > Is it still time for me to submit the v2 of this patch ? I would like do
> add 2 changes:
> > - add fixes:xxx line suggested by Daniel
> > - fix link error for qemu-user build (since it has no access to
> migration code)
>
> I have since noticed the link error indeed, and I'll post a v2 myself
> with the fix.
>
> Next time, if you notice a problem with the patch you should post the
> fixed version without waiting for input.
>

Lesson learnt, thanks !

Hector

>
> Paolo
>
>

[-- Attachment #2: Type: text/html, Size: 1803 bytes --]