KVM: VMX: Allow toggling bits in MSR_IA32_RTIT_CTL when enable bit is cleared

Allow toggling other bits in MSR_IA32_RTIT_CTL if the enable bit is being
cleared, the existing logic simply ignores the enable bit.  E.g. KVM will
incorrectly reject a write of '0' to stop tracing.

Fixes: bf8c55d ("KVM: x86: Implement Intel PT MSRs read/write emulation")
Signed-off-by: Adrian Hunter <[email protected]>
[sean: rework changelog, drop stable@]
Reviewed-by: Xiaoyao Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: ahunter6

arch/x86/kvm/vmx/vmx.c

@@ -1636,7 +1636,8 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data)
 	 * result in a #GP unless the same write also clears TraceEn.
 	 */
 	if ((vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) &&
-		((vmx->pt_desc.guest.ctl ^ data) & ~RTIT_CTL_TRACEEN))
+	    (data & RTIT_CTL_TRACEEN) &&
+	    data != vmx->pt_desc.guest.ctl)
 		return 1;
 
 	/*