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| author | Avi Kivity <avi@qumranet.com> | 2007-04-19 14:28:44 +0300 |
|---|---|---|
| committer | Avi Kivity <avi@qumranet.com> | 2007-05-03 10:52:30 +0300 |
| commit | 4d56c8a787aefb2e3fc4ac4be966db96c14d1ad8 (patch) | |
| tree | 99db1bc065832b2685bd5edb75cd7c1019011ead /drivers/kvm/vmx.c | |
| parent | 35cc7f971188366f5a5c0d5da1456bb38cef5da9 (diff) | |
| download | lwn-4d56c8a787aefb2e3fc4ac4be966db96c14d1ad8.tar.gz lwn-4d56c8a787aefb2e3fc4ac4be966db96c14d1ad8.zip | |
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 <avi@qumranet.com>
Diffstat (limited to 'drivers/kvm/vmx.c')
| -rw-r--r-- | drivers/kvm/vmx.c | 16 |
1 files changed, 16 insertions, 0 deletions
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, |