On Mon, 20 May 2019 at 18:34, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > On 17/05/19 10:49, Wanpeng Li wrote: > > MSR IA32_MSIC_ENABLE bit 18, according to SDM: > > > > | When this bit is set to 0, the MONITOR feature flag is not set (CPUID.01H:ECX[bit 3] = 0). > > | This indicates that MONITOR/MWAIT are not supported. > > | > > | Software attempts to execute MONITOR/MWAIT will cause #UD when this bit is 0. > > | > > | When this bit is set to 1 (default), MONITOR/MWAIT are supported (CPUID.01H:ECX[bit 3] = 1). > > > > The CPUID.01H:ECX[bit 3] ought to mirror the value of the MSR bit, > > CPUID.01H:ECX[bit 3] is a better guard than kvm_mwait_in_guest(). > > kvm_mwait_in_guest() affects the behavior of MONITOR/MWAIT, not its > > guest visibility. > > > > This patch implements toggling of the CPUID bit based on guest writes > > to the MSR. > > Won't this disable mwait after migration, unless IA32_MISC_ENABLE is set > correctly by firmware or userspace? I think you need to hide this Agreed. > behind KVM_CAP_DISABLE_QUIRKS. (Also, what is the reason for this > change in general besides making behavior closer to real hardware?) Just making behavior closer to real hardware. :) Regards, Wanpeng Li
