1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
|
From 885a241a441e144391884136534657f8502b2a48 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 22 Feb 2018 16:43:18 +0100
Subject: [PATCH 33/33] KVM/VMX: Optimize vmx_vcpu_run() and svm_vcpu_run() by
marking the RDMSR path as unlikely()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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@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
Link: http://lkml.kernel.org/r/20180222154318.20361-3-pbonzini@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/svm.c | 2 +-
arch/x86/kvm/vmx.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 8d33396..b82bb66 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5017,7 +5017,7 @@ static void svm_vcpu_run(struct kvm_vcpu *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)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index aa2684a..3c3558b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9024,7 +9024,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *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)))
vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
if (vmx->spec_ctrl)
--
2.7.4
|
