On Mon, Nov 26, 2018 at 03:45:03PM +0100, Igor Mammedov wrote: > On Fri, 21 Sep 2018 11:22:10 +0300 > Roman Kagan <rka...@virtuozzo.com> wrote: > > > Certain configurations do not allow SynIC to be used in QEMU. In > > particular, > > > > - when hyperv_vpindex is off, SINT routes can't be used as they refer to > > the destination vCPU by vp_index > > > > - older KVM (which doesn't expose KVM_CAP_HYPERV_SYNIC2) zeroes out > > SynIC message and event pages on every msr load, breaking migration > > > > OTOH in-KVM users of SynIC -- SynIC timers -- do work in those > > configurations, and we shouldn't stop the guest from using them. > > > > To cover both scenarios, introduce an X86CPU property that makes CPU > > init code to skip creation of the SynIC object (and thus disables any > > SynIC use in QEMU) but keeps the KVM part of the SynIC working. > > The property is clear by default but is set via compat logic for older > > machine types. > > > > As a result, when hv_synic and a modern machine type are specified, QEMU > > will refuse to run unless vp_index is on and the kernel is recent > > enough. OTOH with an older machine type QEMU will run fine with > > hv_synic=on against an older kernel and/or without vp_index enabled but > > will disallow the in-QEMU uses of SynIC (in e.g. VMBus). > > > > Signed-off-by: Roman Kagan <rka...@virtuozzo.com> > > With current upstream and x-hv-synic-kvm-only=on QEMU will SIGSEGV. > Problem was unnoticed since added compat property wasn't actually used > until much later commit > 4a93722f9c hw/i386: add pc-i440fx-3.1 & pc-q35-3.1 > which put compat property in use. > > qemu-system-x86_64 -machine pc-i440fx-2.10,accel=kvm \ > -cpu host,-vmx,hv-relaxed,hv_spinlocks=0x1fff,hv-vpindex,hv-synic > > simpler reproducer: > qemu-system-x86_64 -enable-kvm -cpu host,hv-synic,x-hv-synic-kvm-only=on > > Reported-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
Thanks for the report, fix is on the way to ML. Roman.
