On 21-Aug-24 11:06 AM, Ravi Bangoria wrote: >>> @@ -3158,6 +3159,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) >>> if (data & DEBUGCTL_RESERVED_BITS) >> >> Not your code, but why does DEBUGCTL_RESERVED_BITS = ~0x3f!?!? That means the >> introduction of the below check, which is architecturally correct, has the >> potential to break guests. *sigh* >> >> I doubt it will cause a problem, but it's something to look out for. > This dates back to 2008: https://git.kernel.org/torvalds/c/24e09cbf480a7 > > The legacy definition[1] of DEBUGCTL MSR is: > > 5:2 PB: performance monitor pin control. Read-write. Reset: 0h. > This field does not control any hardware. > 1 BTF. Read-write. Reset: 0. 1=Enable branch single step. > 0 LBR. Read-write. Reset: 0. 1=Enable last branch record. > > [1]: https://bugzilla.kernel.org/attachment.cgi?id=287389 How about adding cpu_feature_enabled() check: if (data & DEBUGCTL_RESERVED_BITS) return 1; if (cpu_feature_enabled(X86_FEATURE_BUS_LOCK_DETECT) && (data & DEBUGCTLMSR_BUS_LOCK_DETECT) && !guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT)) return 1; Thanks, Ravi
