Re: [Qemu-devel] [qemu-s390x] [PATCH v1] s390x/cpu_models: Add "-cpu max" support

[Eduardo Habkost]

On Mon, Jul 30, 2018 at 11:16:38AM +0200, David Hildenbrand wrote:
> On 27.07.2018 14:55, Cornelia Huck wrote:
> > On Wed, 25 Jul 2018 11:12:33 +0200
> > David Hildenbrand <address@hidden> wrote:
> > 
> >> The "max" CPU model behaves like "-cpu host" when KVM is enabled, and like
> >> a CPU with the maximum possible feature set when TCG is enabled.
> >>
> >> While the "host" model can not be used under TCG ("kvm_required"), the
> >> "max" model can and "Enables all features supported by the accelerator in
> >> the current host".
> >>
> >> So we can treat "host" just as a special case of "max" (like x86 does).
> >> It differs to the "qemu" CPU model under TCG such that compatibility
> >> handling will not be performed and that some experimental CPU features
> >> not yet part of the "qemu" model might be indicated.
> >>
> >> These are right now under TCG (see "qemu_MAX"):
> >> - stfle53
> >> - msa5-base
> >> - zpci
> >>
> >> This will result right now in the following warning when starting QEMU TCG
> >> with the "max" model:
> >>     "qemu-system-s390x: warning: 'msa5-base' requires 'kimd-sha-512'."
> >>
> >> The "qemu" model (used as default in QEMU under TCG) will continue to
> >> work without such warnings. The "max" mdel in the current form
> >> might be interesting for kvm-unit-tests (where we would e.g. now also
> >> test "msa5-base").
> >>
> >> The "max" model is neither static nor migration safe (like the "host"
> >> model). It is independent of the machine but dependends on the accelerator.
> >> It can be used to detect the maximum CPU model also under TCG from upper
> >> layers without having to care about CPU model names for CPU model
> >> expansion.
> >>
> >> Signed-off-by: David Hildenbrand <address@hidden>
> >> ---
> >>  target/s390x/cpu_models.c | 81 +++++++++++++++++++++++++++------------
> >>  1 file changed, 56 insertions(+), 25 deletions(-)
> > 
> > So, what's the outcome? Can I merge this with the discussed minor
> > edits, or should I wait for a v2?
> > 
> 
> Eduardo identified possible optimizations independent of this patch, so
> we should be good to go. @Eduardo, please correct me if I'm wrong!

This version still looks good to me, my Reviewed-by line still
applies.  Thanks!

-- 
Eduardo