>> @@ -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 Thanks, Ravi
