[PATCH 3.16 059/410] KVM/x86: Remove indirect MSR op calls from SPEC_CTRL

From: Ben Hutchings
Date: Thu Jun 07 2018 - 10:34:24 EST


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

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

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

commit ecb586bd29c99fb4de599dec388658e74388daad upstream.

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@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: KarimAllah Ahmed <karahmed@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Fixes: d28b387fb74da95d69d2615732f50cceb38e9a4d
Link: http://lkml.kernel.org/r/20180222154318.20361-2-pbonzini@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/svm.c | 7 ++++---
arch/x86/kvm/vmx.c | 7 ++++---
2 files changed, 8 insertions(+), 6 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -36,6 +36,7 @@
#include <asm/desc.h>
#include <asm/debugreg.h>
#include <asm/kvm_para.h>
+#include <asm/microcode.h>
#include <asm/nospec-branch.h>

#include <asm/virtext.h>
@@ -3967,7 +3968,7 @@ static void svm_vcpu_run(struct kvm_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"
@@ -4077,10 +4078,10 @@ static void svm_vcpu_run(struct kvm_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();
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -46,6 +46,7 @@
#include <asm/perf_event.h>
#include <asm/debugreg.h>
#include <asm/kexec.h>
+#include <asm/microcode.h>
#include <asm/nospec-branch.h>

#include "trace.h"
@@ -7542,7 +7543,7 @@ static void __noclone vmx_vcpu_run(struc
* 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(
@@ -7673,10 +7674,10 @@ static void __noclone vmx_vcpu_run(struc
* save it.
*/
if (!msr_write_intercepted_l01(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();