From e38aea3e9330624d19a233c05f3e69c57519edd5 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Thu, 19 Apr 2007 13:22:48 +0300 Subject: KVM: VMX: Don't switch 64-bit msrs for 32-bit guests Some msrs are only used by x86_64 instructions, and are therefore not needed when the guest is legacy mode. By not bothering to switch them, we reduce vmexit latency by 2400 cycles (from about 8800) when running a 32-bt guest on a 64-bit host. Signed-off-by: Avi Kivity --- drivers/kvm/vmx.c | 58 ++++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 42 insertions(+), 16 deletions(-) diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c index 3745e6ccc5b4..6270df58e055 100644 --- a/drivers/kvm/vmx.c +++ b/drivers/kvm/vmx.c @@ -80,6 +80,9 @@ static const u32 vmx_msr_index[] = { #ifdef CONFIG_X86_64 static unsigned msr_offset_kernel_gs_base; +#define NR_64BIT_MSRS 4 +#else +#define NR_64BIT_MSRS 0 #endif static inline int is_page_fault(u32 intr_info) @@ -300,6 +303,32 @@ static void vmx_inject_gp(struct kvm_vcpu *vcpu, unsigned error_code) INTR_INFO_VALID_MASK); } +/* + * Set up the vmcs to automatically save and restore system + * msrs. Don't touch the 64-bit msrs if the guest is in legacy + * mode, as fiddling with msrs is very expensive. + */ +static void setup_msrs(struct kvm_vcpu *vcpu) +{ + int nr_skip, nr_good_msrs; + + if (is_long_mode(vcpu)) + nr_skip = NR_BAD_MSRS; + else + nr_skip = NR_64BIT_MSRS; + nr_good_msrs = vcpu->nmsrs - nr_skip; + + vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR, + virt_to_phys(vcpu->guest_msrs + nr_skip)); + vmcs_writel(VM_EXIT_MSR_STORE_ADDR, + virt_to_phys(vcpu->guest_msrs + nr_skip)); + vmcs_writel(VM_EXIT_MSR_LOAD_ADDR, + virt_to_phys(vcpu->host_msrs + nr_skip)); + vmcs_write32(VM_EXIT_MSR_STORE_COUNT, nr_good_msrs); /* 22.2.2 */ + vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */ + vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */ +} + /* * reads and returns guest's timestamp counter "register" * guest_tsc = host_tsc + tsc_offset -- 21.3 @@ -825,6 +854,7 @@ static void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer) msr->data = efer & ~EFER_LME; } + setup_msrs(vcpu); } #endif @@ -988,7 +1018,6 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu) struct descriptor_table dt; int i; int ret = 0; - int nr_good_msrs; extern asmlinkage void kvm_vmx_return(void); if (!init_rmode_tss(vcpu->kvm)) { @@ -1140,19 +1169,10 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu) ++vcpu->nmsrs; } - nr_good_msrs = vcpu->nmsrs - NR_BAD_MSRS; - vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR, - virt_to_phys(vcpu->guest_msrs + NR_BAD_MSRS)); - vmcs_writel(VM_EXIT_MSR_STORE_ADDR, - virt_to_phys(vcpu->guest_msrs + NR_BAD_MSRS)); - vmcs_writel(VM_EXIT_MSR_LOAD_ADDR, - virt_to_phys(vcpu->host_msrs + NR_BAD_MSRS)); + setup_msrs(vcpu); + vmcs_write32_fixedbits(MSR_IA32_VMX_EXIT_CTLS, VM_EXIT_CONTROLS, (HOST_IS_64 << 9)); /* 22.2,1, 20.7.1 */ - vmcs_write32(VM_EXIT_MSR_STORE_COUNT, nr_good_msrs); /* 22.2.2 */ - vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */ - vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */ - /* 22.2.1, 20.8.1 */ vmcs_write32_fixedbits(MSR_IA32_VMX_ENTRY_CTLS, @@ -1769,9 +1789,11 @@ again: fx_restore(vcpu->guest_fx_image); #ifdef CONFIG_X86_64 - save_msrs(vcpu->host_msrs + msr_offset_kernel_gs_base, 1); + if (is_long_mode(vcpu)) { + save_msrs(vcpu->host_msrs + msr_offset_kernel_gs_base, 1); + load_msrs(vcpu->guest_msrs, NR_BAD_MSRS); + } #endif - load_msrs(vcpu->guest_msrs, NR_BAD_MSRS); asm ( /* Store host registers */ @@ -1915,8 +1937,12 @@ again: } ++kvm_stat.exits; - save_msrs(vcpu->guest_msrs, NR_BAD_MSRS); - load_msrs(vcpu->host_msrs, NR_BAD_MSRS); +#ifdef CONFIG_X86_64 + if (is_long_mode(vcpu)) { + save_msrs(vcpu->guest_msrs, NR_BAD_MSRS); + load_msrs(vcpu->host_msrs, NR_BAD_MSRS); + } +#endif fx_save(vcpu->guest_fx_image); fx_restore(vcpu->host_fx_image); -- cgit v1.2.3-59-g8ed1b