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 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 946fbbc13dce68902f64515b610eeb2a6c3d7a64 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini pbonzini@redhat.com 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() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
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
--- 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 @@ -5139,7 +5139,7 @@ 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 @@ -9579,7 +9579,7 @@ 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@redhat.com are
queue-4.15/kvm-x86-fix-smram-accessing-even-if-vm-is-shutdown.patch queue-4.15/kvm-x86-remove-indirect-msr-op-calls-from-spec_ctrl.patch queue-4.15/kvm-x86-move-lapic-initialization-after-vmcs-creation.patch queue-4.15/kvm-mmu-fix-overlap-between-public-and-private-memslots.patch queue-4.15/kvm-vmx-optimize-vmx_vcpu_run-and-svm_vcpu_run-by-marking-the-rdmsr-path-as-unlikely.patch