linux-kernel - [PATCH 3.16 366/370] Revert "KVM: x86: expose MSR_TSC

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Message-ID: <lsq.1489146383.267063808@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:23 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eric Wheeler" <kvm@...ts.ewheeler.net>
Subject: [PATCH 3.16 366/370] Revert "KVM: x86: expose MSR_TSC_AUX to
 userspace"

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@...adent.org.uk>

This reverts commit a79ed0ed3763b3558b74e7d65fdd8c0215b5b6a2, which was
commit 9dbe6cf941a6fe82933aef565e4095fb10f65023 upstream.  It depends on
several other large commits to work, and without them causes a regression.

References: https://bugzilla.redhat.com/show_bug.cgi?id=1408333
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Cc: Eric Wheeler <kvm@...ts.ewheeler.net>
---
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -892,7 +892,7 @@ 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_TSC_AUX,
+	MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS
 };
 
 static unsigned num_msrs_to_save;
@@ -3994,17 +3994,16 @@ 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.
+		 * 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.
 		 */
 		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;
 		}