On Mon, Jul 12, 2021 at 3:19 AM Like Xu <like.xu.linux@xxxxxxxxx> wrote: > > On 12/7/2021 5:53 pm, Yang Weijiang wrote: > > On Fri, Jul 09, 2021 at 04:41:30PM -0700, Jim Mattson wrote: > >> On Fri, Jul 9, 2021 at 3:54 PM Jim Mattson <jmattson@xxxxxxxxxx> wrote: > >>> > >>> On Fri, Jul 9, 2021 at 2:51 AM Yang Weijiang <weijiang.yang@xxxxxxxxx> wrote: > >>>> > >>>> If host is using MSR_ARCH_LBR_CTL then save it before vm-entry > >>>> and reload it after vm-exit. > >>> > >>> I don't see anything being done here "before VM-entry" or "after > >>> VM-exit." This code seems to be invoked on vcpu_load and vcpu_put. > >>> > >>> In any case, I don't see why this one MSR is special. It seems that if > >>> the host is using the architectural LBR MSRs, then *all* of the host > >>> architectural LBR MSRs have to be saved on vcpu_load and restored on > >>> vcpu_put. Shouldn't kvm_load_guest_fpu() and kvm_put_guest_fpu() do > >>> that via the calls to kvm_save_current_fpu(vcpu->arch.user_fpu) and > >>> restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state)? > >> > >> It does seem like there is something special about IA32_LBR_DEPTH, though... > >> > >> Section 7.3.1 of the Intel® Architecture Instruction Set Extensions > >> and Future Features Programming Reference > >> says, "IA32_LBR_DEPTH is saved by XSAVES, but it is not written by > >> XRSTORS in any circumstance." It seems like that would require some > >> special handling if the host depth and the guest depth do not match. > > In our vPMU design, guest depth is alway kept the same as that of host, > > so this won't be a problem. But I'll double check the code again, thanks! > > KVM only exposes the host's depth value to the user space > so the guest can only use the same depth as the host. The allowed depth supplied by KVM_GET_SUPPORTED_CPUID isn't enforced, though, is it?
