KVM/VMX: Optimize vmx_vcpu_run() and svm_vcpu_run() by marking the RDMSR path as...

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 <[email protected]>
Reviewed-by: Jim Mattson <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: KarimAllah Ahmed <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1598beeda11c1d6dd4e1aabe2e53ceea8b22f2f7..24c9521ebc24624ee35fe4893e06111a914b897a 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5465,7 +5465,7 @@ 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 0927be315965b3548b5250b6ac47a6189978bea1..7f8401d059390733d85f4e9dc8265443c5f3f915 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9588,7 +9588,7 @@ 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)