On Mon, Jul 12, 2021 at 10:20:04AM -0700, Jim Mattson wrote: > 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? Do you mean to enforce a check to depth written from user space via KVM_SET_CPUID2?
