On 29/05/20 14:08, Vitaly Kuznetsov wrote:

quoted

On 24/04/20 13:37, Jon Doron wrote:

quoted

+static int syndbg_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host)
+{
+	struct kvm_hv_syndbg *syndbg = vcpu_to_hv_syndbg(vcpu);
+
+	if (!syndbg->active && !host)
+		return 1;
+

One small thing: is the ENABLE_CAP and active field needed?  Can you
just check if the guest has the syndbg CPUID bits set?

Yes, we can probably get away with a static capability (so userspace
knows that the interface is supported and CPUID bit can be set) and
check guest_cpuid_has() here but we don't have Hyper-V feature leaves
exposed as X86_FEATURE_* (yet). It is probably possible to implement an
interim solution by open coding the check with kvm_find_cpuid_entry() or
something like that.

Yes, that would be fine if you just abstract it in its own function.

Paolo