From 4d56c8a787aefb2e3fc4ac4be966db96c14d1ad8 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Thu, 19 Apr 2007 14:28:44 +0300 Subject: [PATCH] KVM: VMX: Only save/restore MSR_K6_STAR if necessary Intel hosts only support syscall/sysret in long more (and only if efer.sce is enabled), so only reload the related MSR_K6_STAR if the guest will actually be able to use it. This reduces vmexit cost by about 500 cycles (6400 -> 5870) on my setup. Signed-off-by: Avi Kivity --- drivers/kvm/vmx.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c index b61d4dd804e3..37537af126d1 100644 --- a/drivers/kvm/vmx.c +++ b/drivers/kvm/vmx.c @@ -69,6 +69,10 @@ static struct kvm_vmx_segment_field { VMX_SEGMENT_FIELD(LDTR), }; +/* + * Keep MSR_K6_STAR at the end, as setup_msrs() will try to optimize it + * away by decrementing the array size. + */ static const u32 vmx_msr_index[] = { #ifdef CONFIG_X86_64 MSR_SYSCALL_MASK, MSR_LSTAR, MSR_CSTAR, MSR_KERNEL_GS_BASE, @@ -323,6 +327,18 @@ static void setup_msrs(struct kvm_vcpu *vcpu) nr_skip = NR_64BIT_MSRS; nr_good_msrs = vcpu->nmsrs - nr_skip; + /* + * MSR_K6_STAR is only needed on long mode guests, and only + * if efer.sce is enabled. + */ + if (find_msr_entry(vcpu, MSR_K6_STAR)) { + --nr_good_msrs; +#ifdef CONFIG_X86_64 + if (is_long_mode(vcpu) && (vcpu->shadow_efer & EFER_SCE)) + ++nr_good_msrs; +#endif + } + vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR, virt_to_phys(vcpu->guest_msrs + nr_skip)); vmcs_writel(VM_EXIT_MSR_STORE_ADDR,