This is a note to let you know that I've just added the patch titled
KVM/VMX: Optimize vmx_vcpu_run() and svm_vcpu_run() by marking the RDMSR path as unlikely()
to the 4.9-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-vmx-optimize-vmx_vcpu_run-and-svm_vcpu_run-by-marking-the-rdmsr-path-as-unlikely.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 946fbbc13dce68902f64515b610eeb2a6c3d7a64 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Thu, 22 Feb 2018 16:43:18 +0100
Subject: KVM/VMX: Optimize vmx_vcpu_run() and svm_vcpu_run() by marking the RDMSR path as unlikely()
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From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
commit 946fbbc13dce68902f64515b610eeb2a6c3d7a64 upstream.
vmx_vcpu_run() and svm_vcpu_run() are large functions, and giving
branch hints to the compiler can actually make a substantial cycle
difference by keeping the fast path contiguous in memory.
With this optimization, the retpoline-guest/retpoline-host case is
about 50 cycles faster.
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 Krčmář <rkrcmar@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20180222154318.20361-3-pbonzini@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/svm.c | 2 +-
arch/x86/kvm/vmx.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5029,7 +5029,7 @@ static void svm_vcpu_run(struct kvm_vcpu
* If the L02 MSR bitmap does not intercept the MSR, then we need to
* save it.
*/
- if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
+ if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
if (svm->spec_ctrl)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9042,7 +9042,7 @@ static void __noclone vmx_vcpu_run(struc
* If the L02 MSR bitmap does not intercept the MSR, then we need to
* save it.
*/
- if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
+ if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
if (vmx->spec_ctrl)
Patches currently in stable-queue which might be from pbonzini@xxxxxxxxxx are
queue-4.9/kvm-x86-fix-smram-accessing-even-if-vm-is-shutdown.patch
queue-4.9/kvm-x86-remove-indirect-msr-op-calls-from-spec_ctrl.patch
queue-4.9/kvm-mmu-fix-overlap-between-public-and-private-memslots.patch
queue-4.9/kvm-vmx-optimize-vmx_vcpu_run-and-svm_vcpu_run-by-marking-the-rdmsr-path-as-unlikely.patch