From: Paolo Bonzini pbonzini@redhat.com

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 [Yi Sun: cherry pick to 4.4] Signed-off-by: Yi Sun yi.y.sun@linux.intel.com --- 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 cb46661..35da1e2 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -4017,7 +4017,7 @@ 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 6c109df..1f165cc 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -8743,7 +8743,7 @@ 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)