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Date: Fri, 15 Oct 2021 00:01:22 +0000 From: Sean Christopherson <seanjc@...gle.com> To: Yang Weijiang <weijiang.yang@...el.com> Cc: pbonzini@...hat.com, jmattson@...gle.com, like.xu.linux@...il.com, vkuznets@...hat.com, wei.w.wang@...el.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v8 15/15] KVM: x86/cpuid: Advise Arch LBR feature in CPUID s/Advise/Advertise On Tue, Aug 24, 2021, Yang Weijiang wrote: > Add Arch LBR feature bit in CPU cap-mask to expose the feature. > Only max LBR depth is supported for guest, and it's consistent > with host Arch LBR settings. > > Co-developed-by: Like Xu <like.xu@...ux.intel.com> > Signed-off-by: Like Xu <like.xu@...ux.intel.com> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com> > --- > arch/x86/kvm/cpuid.c | 33 ++++++++++++++++++++++++++++++++- > 1 file changed, 32 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 03025eea1524..d98ebefd5d72 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -88,6 +88,16 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent) > if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0) > return -EINVAL; > } > + best = cpuid_entry2_find(entries, nent, 0x1c, 0); > + if (best) { > + unsigned int eax, ebx, ecx, edx; > + > + /* Reject user-space CPUID if depth is different from host's.*/ Why disallow this? I don't see why it would be illegal for userspace to specify fewer LBRs, and KVM should darn well verify that any MSRs it's exposing to the guest actually exist. > + cpuid_count(0x1c, 0, &eax, &ebx, &ecx, &edx); > + > + if ((best->eax & 0xff) != BIT(fls(eax & 0xff) - 1)) > + return -EINVAL; > + } > > return 0; > }
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