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   1 From 946fbbc13dce68902f64515b610eeb2a6c3d7a64 Mon Sep 17 00:00:00 2001
   2 From: Paolo Bonzini <pbonzini@redhat.com>
   3 Date: Thu, 22 Feb 2018 16:43:18 +0100
   4 Subject: KVM/VMX: Optimize vmx_vcpu_run() and svm_vcpu_run() by marking the RDMSR path as unlikely()
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   8
   9 From: Paolo Bonzini <pbonzini@redhat.com>
  10
  11 commit 946fbbc13dce68902f64515b610eeb2a6c3d7a64 upstream.
  12
  13 vmx_vcpu_run() and svm_vcpu_run() are large functions, and giving
  14 branch hints to the compiler can actually make a substantial cycle
  15 difference by keeping the fast path contiguous in memory.
  16
  17 With this optimization, the retpoline-guest/retpoline-host case is
  18 about 50 cycles faster.
  19
  20 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  21 Reviewed-by: Jim Mattson <jmattson@google.com>
  22 Cc: David Woodhouse <dwmw@amazon.co.uk>
  23 Cc: KarimAllah Ahmed <karahmed@amazon.de>
  24 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  25 Cc: Peter Zijlstra <peterz@infradead.org>
  26 Cc: Radim Krčmář <rkrcmar@redhat.com>
  27 Cc: Thomas Gleixner <tglx@linutronix.de>
  28 Cc: kvm@vger.kernel.org
  29 Cc: stable@vger.kernel.org
  30 Link: http://lkml.kernel.org/r/20180222154318.20361-3-pbonzini@redhat.com
  31 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  32 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  33
  34 ---
  35  arch/x86/kvm/svm.c |    2 +-
  36  arch/x86/kvm/vmx.c |    2 +-
  37  2 files changed, 2 insertions(+), 2 deletions(-)
  38
  39 --- a/arch/x86/kvm/svm.c
  40 +++ b/arch/x86/kvm/svm.c
  41 @@ -5029,7 +5029,7 @@ static void svm_vcpu_run(struct kvm_vcpu
  42          * If the L02 MSR bitmap does not intercept the MSR, then we need to
  43          * save it.
  44          */
  45 -       if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
  46 +       if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
  47                 svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
  48
  49         if (svm->spec_ctrl)
  50 --- a/arch/x86/kvm/vmx.c
  51 +++ b/arch/x86/kvm/vmx.c
  52 @@ -9042,7 +9042,7 @@ static void __noclone vmx_vcpu_run(struc
  53          * If the L02 MSR bitmap does not intercept the MSR, then we need to
  54          * save it.
  55          */
  56 -       if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
  57 +       if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
  58                 vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
  59
  60         if (vmx->spec_ctrl)