Patch "KVM: x86: expose MSR_TSC_AUX to userspace" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

KVM: x86: expose MSR_TSC_AUX to userspace

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-expose-msr_tsc_aux-to-userspace.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paolo Bonzini <[email protected]>
Date: Thu, 12 Nov 2015 14:49:17 +0100
Subject: KVM: x86: expose MSR_TSC_AUX to userspace

From: Paolo Bonzini <[email protected]>

commit 9dbe6cf941a6fe82933aef565e4095fb10f65023 upstream.

If we do not do this, it is not properly saved and restored across migration. Windows notices due to its self-protection mechanisms, and is very upset about it (blue screen of death).

---
 arch/x86/kvm/x86.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

@@ -942,7 +942,7 @@ static u32 msrs_to_save[] = {
 	MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
 #endif
 	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
-	MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS
+	MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
 };
 
 static unsigned num_msrs_to_save;

@@ -3847,16 +3847,17 @@ static void kvm_init_msr_list(void)
 
 		/*
 		 * Even MSRs that are valid in the host may not be exposed
-		 * to the guests in some cases.  We could work around this
-		 * in VMX with the generic MSR save/load machinery, but it
-		 * is not really worthwhile since it will really only
-		 * happen with nested virtualization.
+		 * to the guests in some cases.
 		 */
 		switch (msrs_to_save[i]) {
 		case MSR_IA32_BNDCFGS:
 			if (!kvm_x86_ops->mpx_supported())
 				continue;
 			break;
+		case MSR_TSC_AUX:
+			if (!kvm_x86_ops->rdtscp_supported())
+				continue;
+			break;
 		default:
 			break;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/kvm-x86-correctly-print-ac-in-traces.patch queue-4.3/kvm-vmx-fix-smep-and-smap-without-ept.patch queue-4.3/kvm-x86-expose-msr_tsc_aux-to-userspace.patch queue-4.3/kvm-svm-unconditionally-intercept-db.patch