KVM/x86: Remove indirect MSR op calls from SPEC_CTRL

Having a paravirt indirect call in the IBRS restore path is not a
good idea, since we are trying to protect from speculative execution
of bogus indirect branch targets.  It is also slower, so use
native_wrmsrl() on the vmentry path too.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: d28b387fb74da95d69d2615732f50cceb38e9a4d
Link: http://lkml.kernel.org/r/20180222154318.20361-2-pbonzini@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 8 insertions, 6 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index b3e488a74828..1598beeda11c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -49,6 +49,7 @@
 #include <asm/debugreg.h>
 #include <asm/kvm_para.h>
 #include <asm/irq_remapping.h>
+#include <asm/microcode.h>
 #include <asm/nospec-branch.h>
 
 #include <asm/virtext.h>
@@ -5355,7 +5356,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
          * being speculatively taken.
          */
         if (svm->spec_ctrl)
-                wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+                native_wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
 
         asm volatile (
                 "push %%" _ASM_BP "; \n\t"
@@ -5465,10 +5466,10 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
          * save it.
          */
         if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
-                rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+                svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
         if (svm->spec_ctrl)
-                wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+                native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
 
         /* Eliminate branch target predictions from guest mode */
         vmexit_fill_RSB();
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3dec126aa302..0927be315965 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -51,6 +51,7 @@
 #include <asm/apic.h>
 #include <asm/irq_remapping.h>
 #include <asm/mmu_context.h>
+#include <asm/microcode.h>
 #include <asm/nospec-branch.h>
 
 #include "trace.h"
@@ -9452,7 +9453,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
          * being speculatively taken.
          */
         if (vmx->spec_ctrl)
-                wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
+                native_wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
 
         vmx->__launched = vmx->loaded_vmcs->launched;
         asm(
@@ -9588,10 +9589,10 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
          * save it.
          */
         if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
-                rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
+                vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
         if (vmx->spec_ctrl)
-                wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+                native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
 
         /* Eliminate branch target predictions from guest mode */
         vmexit_fill_RSB();