On Thu, Jul 02, 2020 at 08:44:55PM +0300, Maxim Levitsky wrote: > There are few cases when this function was creating a bogus #GP condition, > for example case when and AMD host supports STIBP but doesn't support SSBD. > > Follow the rules for AMD and Intel strictly instead.
Can you elaborate on the conditions that are problematic, e.g. what does the guest expect to exist that KVM isn't providing? > AMD #GP rules for IA32_SPEC_CTRL can be found here: > https://bugzilla.kernel.org/show_bug.cgi?id=199889 > > Fixes: 6441fa6178f5 ("KVM: x86: avoid incorrect writes to host > MSR_IA32_SPEC_CTRL") > > Signed-off-by: Maxim Levitsky <[email protected]> > --- > arch/x86/kvm/x86.c | 57 ++++++++++++++++++++++++++++++++++------------ > 1 file changed, 42 insertions(+), 15 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 00c88c2f34e4..a6bed4670b7f 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -10670,27 +10670,54 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) > } > EXPORT_SYMBOL_GPL(kvm_arch_no_poll); > > -u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu) > + > +static u64 kvm_spec_ctrl_valid_bits_host(void) > +{ > + uint64_t bits = 0; > + > + if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) > + bits |= SPEC_CTRL_IBRS; > + if (boot_cpu_has(X86_FEATURE_INTEL_STIBP)) > + bits |= SPEC_CTRL_STIBP; > + if (boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD)) > + bits |= SPEC_CTRL_SSBD; > + > + if (boot_cpu_has(X86_FEATURE_AMD_IBRS) || > boot_cpu_has(X86_FEATURE_AMD_STIBP)) > + bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS; > + > + if (boot_cpu_has(X86_FEATURE_AMD_SSBD)) > + bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS | SPEC_CTRL_SSBD; > + > + return bits; > +} Rather than compute the mask every time, it can be computed once on module load and stashed in a global. Note, there's a RFC series[*] to support reprobing bugs at runtime, but that has bigger issues with existing KVM functionality to be addressed, i.e. it's not our problem, yet :-). [*] https://lkml.kernel.org/r/[email protected] > + > +static u64 kvm_spec_ctrl_valid_bits_guest(struct kvm_vcpu *vcpu) > { > - uint64_t bits = SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD; > + uint64_t bits = 0; > > - /* The STIBP bit doesn't fault even if it's not advertised */ > - if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) && > - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS)) > - bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP); > - if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL) && > - !boot_cpu_has(X86_FEATURE_AMD_IBRS)) > - bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP); > + if (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)) > + bits |= SPEC_CTRL_IBRS; > + if (guest_cpuid_has(vcpu, X86_FEATURE_INTEL_STIBP)) > + bits |= SPEC_CTRL_STIBP; > + if (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD)) > + bits |= SPEC_CTRL_SSBD; > > - if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD) && > - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) > - bits &= ~SPEC_CTRL_SSBD; > - if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) && > - !boot_cpu_has(X86_FEATURE_AMD_SSBD)) > - bits &= ~SPEC_CTRL_SSBD; > + if (guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) || > + guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP)) Bad indentation. > + bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS; > + if (guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) > + bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS | SPEC_CTRL_SSBD; Would it be feasible to split into two patches? The first (tagged Fixes:) to make the functional changes without inverting the logic or splitting, and then do the cleanup? It's really hard to review this patch because I can't easily tease out what's different in terms of functionality. > return bits; > } > + > +u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu) > +{ > + return kvm_spec_ctrl_valid_bits_host() & > + kvm_spec_ctrl_valid_bits_guest(vcpu); > +} > + > + > EXPORT_SYMBOL_GPL(kvm_spec_ctrl_valid_bits); > > EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit); > -- > 2.25.4 >
