Patch "KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL" has been added to the 4.14-stable tree

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

KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL

to the 4.14-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:
KVMVMX_Allow_direct_access_to_MSR_IA32_SPEC_CTRL.patch
and it can be found in the queue-4.14 subdirectory.

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

Subject: KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL
From: KarimAllah Ahmed [email protected]
Date: Thu Feb 1 22:59:45 2018 +0100

From: KarimAllah Ahmed [email protected]

commit d28b387fb74da95d69d2615732f50cceb38e9a4d

[ Based on a patch from Ashok Raj <[email protected]> ]

Add direct access to MSR_IA32_SPEC_CTRL for guests. This is needed for guests that will only mitigate Spectre V2 through IBRS+IBPB and will not be using a retpoline+IBPB based approach.

To avoid the overhead of saving and restoring the MSR_IA32_SPEC_CTRL for guests that do not actually use the MSR, only start saving and restoring when a non-zero is written to it.

No attempt is made to handle STIBP here, intentionally. Filtering STIBP may be added in a future patch, which may require trapping all writes if we don't want to pass it through directly to the guest.

[dwmw2: Clean up CPUID bits, save/restore manually, handle reset]

---
 arch/x86/kvm/cpuid.c |    9 ++--
 arch/x86/kvm/vmx.c   |  105 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/x86.c   |    2 
 3 files changed, 110 insertions(+), 6 deletions(-)

@@ -367,7 +367,7 @@ static inline int __do_cpuid_ent(struct
 
 	/* cpuid 0x80000008.ebx */
 	const u32 kvm_cpuid_8000_0008_ebx_x86_features =
-		F(IBPB);
+		F(IBPB) | F(IBRS);
 
 	/* cpuid 0xC0000001.edx */
 	const u32 kvm_cpuid_C000_0001_edx_x86_features =

@@ -394,7 +394,8 @@ static inline int __do_cpuid_ent(struct
 
 	/* cpuid 7.0.edx*/
 	const u32 kvm_cpuid_7_0_edx_x86_features =
-		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(ARCH_CAPABILITIES);
+		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
+		F(ARCH_CAPABILITIES);
 
 	/* all calls to cpuid_count() should be made on the same cpu */
 	get_cpu();

@@ -630,9 +631,11 @@ static inline int __do_cpuid_ent(struct
 			g_phys_as = phys_as;
 		entry->eax = g_phys_as | (virt_as << 8);
 		entry->edx = 0;
-		/* IBPB isn't necessarily present in hardware cpuid */
+		/* IBRS and IBPB aren't necessarily present in hardware cpuid */
 		if (boot_cpu_has(X86_FEATURE_IBPB))
 			entry->ebx |= F(IBPB);
+		if (boot_cpu_has(X86_FEATURE_IBRS))
+			entry->ebx |= F(IBRS);
 		entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features;
 		cpuid_mask(&entry->ebx, CPUID_8000_0008_EBX);
 		break;

@@ -1006,7 +1006,7 @@ static u32 msrs_to_save[] = {
 #endif
 	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
 	MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
-	MSR_IA32_ARCH_CAPABILITIES
+	MSR_IA32_SPEC_CTRL, MSR_IA32_ARCH_CAPABILITIES
 };
 
 static unsigned num_msrs_to_save;

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

queue-4.14/x86pti_Do_not_enable_PTI_on_CPUs_which_are_not_vulnerable_to_Meltdown.patch queue-4.14/x86cpufeature_Blacklist_SPEC_CTRLPRED_CMD_on_early_Spectre_v2_microcodes.patch queue-4.14/x86cpufeatures_Add_Intel_feature_bits_for_Speculation_Control.patch queue-4.14/x86paravirt_Remove_noreplace-paravirt_cmdline_option.patch queue-4.14/KVM_VMX_Make_indirect_call_speculation_safe.patch queue-4.14/x86msr_Add_definitions_for_new_speculation_control_MSRs.patch queue-4.14/KVMVMX_Allow_direct_access_to_MSR_IA32_SPEC_CTRL.patch queue-4.14/x86cpufeatures_Add_CPUID_7_EDX_CPUID_leaf.patch queue-4.14/x86cpufeatures_Add_AMD_feature_bits_for_Speculation_Control.patch queue-4.14/KVMSVM_Allow_direct_access_to_MSR_IA32_SPEC_CTRL.patch queue-4.14/KVMx86_Add_IBPB_support.patch queue-4.14/KVMVMX_Emulate_MSR_IA32_ARCH_CAPABILITIES.patch queue-4.14/x86speculation_Add_basic_IBPB_(Indirect_Branch_Prediction_Barrier)_support.patch queue-4.14/KVM_x86_Make_indirect_calls_in_emulator_speculation_safe.patch