Re: [libvirt PATCH 4/5] qemu: probe for "-cpu max" support

On Tue, Feb 09, 2021 at 05:23:35PM +0100, Pavel Hrdina wrote: > On Tue, Feb 09, 2021 at 01:59:00PM +0000, Daniel P. Berrangé wrote: > > This is a special CPU model similar to "-cpu host", so won't use our > > normal CPU model detection logic. > > > > Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; > > --- > > src/qemu/qemu_capabilities.c | 11 +++++++++++ > > src/qemu/qemu_capabilities.h | 1 + > > 2 files changed, 12 insertions(+) > > > > diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c > > index d0378f94bc..ecfb313d0a 100644 > > --- a/src/qemu/qemu_capabilities.c > > +++ b/src/qemu/qemu_capabilities.c > > @@ -614,6 +614,7 @@ VIR_ENUM_IMPL(virQEMUCaps, > > > > /* 390 */ > > "vhost-user-blk", > > + "cpu-max", > > ); > > > > > > @@ -2984,12 +2985,22 @@ virQEMUCapsProbeQMPCPUDefinitions(virQEMUCapsPtr qemuCaps, > > virQEMUCapsAccelPtr accel, > > qemuMonitorPtr mon) > > { > > + qemuMonitorCPUDefsPtr defs = accel->cpuModels; > > accel->cpuModels is NULL here ... [0] > > > + size_t i; > > + > > if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_CPU_DEFINITIONS)) > > return 0; > > > > if (virQEMUCapsFetchCPUDefinitions(mon, qemuCaps->arch, &accel->cpuModels) < 0) > > return -1; > > > > + for (i = 0; i < defs->ncpus; i++) { > > [0] ... so here it will crash. > > > + if (STREQ_NULLABLE(defs->cpus[i].name, "max")) { > > + virQEMUCapsSet(qemuCaps, QEMU_CAPS_CPU_MAX); > > + break; > > + } > > + } > > + > > Do we trust QEMU that if accel=kvm supports cpu-max that accel=tcg > supports it as well and is that true on all architectures? Yes, it would be considered a bug if that wasn't the case, because the whole point of "max" is that it works for KVM and TCG.