Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

On 07/24/2018 12:59 PM, Daniel P. Berrangé wrote: > On Tue, Jul 24, 2018 at 06:53:54PM +0200, Cornelia Huck wrote: >> On Tue, 24 Jul 2018 18:08:21 +0200 >> Jiri Denemark <jdenemar(a)redhat.com&gt; wrote: >> >>> On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote: >>>> Use model name "qemu" instead of "max" when calling >>>> query-cpu-model-expansion for s390 on tcg. >>>> >>>> Signed-off-by: Collin Walling <walling(a)linux.ibm.com&gt; >>>> --- >>>> src/qemu/qemu_capabilities.c | 5 ++++- >>>> 1 file changed, 4 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c >>>> index 23b4833..e9b44cc 100644 >>>> --- a/src/qemu/qemu_capabilities.c >>>> +++ b/src/qemu/qemu_capabilities.c >>>> @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps, >>>> >>>> if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) { >>>> virtType = VIR_DOMAIN_VIRT_QEMU; >>>> - model = "max"; >>>> + if (ARCH_IS_S390(qemuCaps->arch)) >>>> + model = "qemu"; >>>> + else >>>> + model = "max"; >>> >>> I think we should also check if "max" is a supported model >>> (qemuCaps->tcgCPUModels is already populated at this point) and only use >>> "qemu" on s390 if "max" is not supported. And please, report the issue >>> to QEMU developers since one of the reasons behind "max" is its >>> universal availability on everywhere CPU model expansion is supported. >> >> Hm, can you point me to that discussion? A quick search through the >> QEMU log gives me the addition of the "max" model on i386 as a >> replacement to the "host" model for !kvm, but nothing about it being >> universal... > > I don't recall the link but "max" is supposed to be the standard shorthand > for "enable all the features supported by the virt type". IOW, 'max' should > work both KVM and TCG ("host" was only well defined for KVM), and across > all architectures. > > So having to use a different name on s390 is a bug in QEMU imho. > > Regards, > Daniel > Thanks for expanding on what the "max" model name is suppose to be. I wonder if a s/"qemu"/"max" in QEMU would suffice (I'm taking a shot in the dark here.)

@Connie, @David, you both are far more knowledgeable in this area than I am. What do either of you suggest for moving forward with this? Should we forward this discussion on qemu-devel?