On Wed, Apr 18, 2018 at 11:24:22AM +0800, Wanpeng Li wrote: > 2018-04-18 4:24 GMT+08:00 Eduardo Habkost <ehabkost@xxxxxxxxxx>: > > On Tue, Apr 17, 2018 at 06:40:58PM +0800, Wanpeng Li wrote: > >> Cc Eduardo, > >> 2018-02-26 20:41 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > >> > On 26/02/2018 13:22, Borislav Petkov wrote: > >> >> On Mon, Feb 26, 2018 at 01:18:07PM +0100, Paolo Bonzini wrote: > >> >>>> In this context, "host-initiated" write means written by KVM userspace > >> >>>> with ioctl(KVM_SET_MSR). It generally happens only on VM startup, reset > >> >>>> or live migration. > >> >>> > >> >>> To be clear, the target of the write is still the vCPU's emulated MSR. > >> >> > >> >> So how am I to imagine this as a user: > >> >> > >> >> qemu-system-x86_64 --microcode-revision=0xdeadbeef... > >> > > >> > More like "-cpu foo,ucode_rev=0xdeadbeef". But in practice what would > >> > happen is one of the following: > >> > > >> > 1) "-cpu host" sets ucode_rev to the same value of the host, everyone > >> > else leaves it to zero as is now. > >> > >> Hi Paolo, > >> > >> Do you mean the host admin to get the ucode_rev from the host and set > >> to -cpu host, ucode_rev=xxxxxx or qemu get the ucode_rev directly by > >> rdmsr? > > > > QEMU setting ucode_rev automatically using the host value when > > using "-cpu host" (with no need for explicit ucode_rev option) > > makes sense to me. > > QEMU can't get the host value by rdmsr MSR_IA32_UCODE_REV directly > since rdmsr will #GP when ring !=0, any idea? By looking at kvm_get_msr_feature(), it looks like ioctl(system_fd, KVM_GET_MSRS) would return the host MSR value for us. -- Eduardo
