[PATCH 4/4] KVM: VMX: Use shared msr infrastructure

Avi Kivity
2009-09-16T12:45:44Z

Instead of reloading syscall MSRs on every preemption, use the new shared
msr infrastructure to reload them at the last possible minute (just before
exit to userspace).

Improves vcpu/idle/vcpu switches by about 2000 cycles (when EFER needs to be
reloaded as well).

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/vmx.c | 108 +++++++++++++++++++--------------------------------
1 files changed, 40 insertions(+), 68 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 547881a..8dae1dc 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -67,6 +67,11 @@ struct vmcs {
char data[0];
};

+struct shared_msr_entry {
+ unsigned index;
+ u64 data;
+};
+
struct vcpu_vmx {
struct kvm_vcpu vcpu;
struct list_head local_vcpus_link;
@@ -74,8 +79,7 @@ struct vcpu_vmx {
int launched;
u8 fail;
u32 idt_vectoring_info;
- struct kvm_msr_entry *guest_msrs;
- struct kvm_msr_entry *host_msrs;
+ struct shared_msr_entry *guest_msrs;
int nmsrs;
int save_nmsrs;
int msr_offset_efer;
@@ -89,7 +93,6 @@ struct vcpu_vmx {
u16 fs_sel, gs_sel, ldt_sel;
int gs_ldt_reload_needed;
int fs_reload_needed;
- int guest_efer_loaded;
} host_state;
struct {
int vm86_active;
@@ -176,6 +179,8 @@ static struct kvm_vmx_segment_field {
VMX_SEGMENT_FIELD(LDTR),
};

+static u64 host_efer;
+
static void ept_save_pdptrs(struct kvm_vcpu *vcpu);

/*
@@ -190,22 +195,6 @@ static const u32 vmx_msr_index[] = {
};
#define NR_VMX_MSR ARRAY_SIZE(vmx_msr_index)

-static void load_msrs(struct kvm_msr_entry *e, int n)
-{
- int i;
-
- for (i = 0; i < n; ++i)
- wrmsrl(e[i].index, e[i].data);
-}
-
-static void save_msrs(struct kvm_msr_entry *e, int n)
-{
- int i;
-
- for (i = 0; i < n; ++i)
- rdmsrl(e[i].index, e[i].data);
-}
-
static inline int is_page_fault(u32 intr_info)
{
return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK |
@@ -348,7 +337,7 @@ static int __find_msr_index(struct vcpu_vmx *vmx, u32 msr)
int i;

for (i = 0; i < vmx->nmsrs; ++i)
- if (vmx->guest_msrs[i].index == msr)
+ if (vmx_msr_index[vmx->guest_msrs[i].index] == msr)
return i;
return -1;
}
@@ -379,7 +368,7 @@ static inline void __invept(int ext, u64 eptp, gpa_t gpa)
: : "a" (&operand), "c" (ext) : "cc", "memory");
}

-static struct kvm_msr_entry *find_msr_entry(struct vcpu_vmx *vmx, u32 msr)
+static struct shared_msr_entry *find_msr_entry(struct vcpu_vmx *vmx, u32 msr)
{
int i;

@@ -570,17 +559,15 @@ static void reload_tss(void)
load_TR_desc();
}

-static void load_transition_efer(struct vcpu_vmx *vmx)
+static bool update_transition_efer(struct vcpu_vmx *vmx)
{
int efer_offset = vmx->msr_offset_efer;
- u64 host_efer;
u64 guest_efer;
u64 ignore_bits;

if (efer_offset < 0)
- return;
- host_efer = vmx->host_msrs[efer_offset].data;
- guest_efer = vmx->guest_msrs[efer_offset].data;
+ return false;
+ guest_efer = vmx->vcpu.arch.shadow_efer;

/*
* NX is emulated; LMA and LME handled by hardware; SCE meaninless
@@ -594,26 +581,18 @@ static void load_transition_efer(struct vcpu_vmx *vmx)
ignore_bits &= ~(u64)EFER_SCE;
#endif
if ((guest_efer & ~ignore_bits) == (host_efer & ~ignore_bits))
- return;
+ return false;

- vmx->host_state.guest_efer_loaded = 1;
guest_efer &= ~ignore_bits;
guest_efer |= host_efer & ignore_bits;
- wrmsrl(MSR_EFER, guest_efer);
- vmx->vcpu.stat.efer_reload++;
-}
-
-static void reload_host_efer(struct vcpu_vmx *vmx)
-{
- if (vmx->host_state.guest_efer_loaded) {
- vmx->host_state.guest_efer_loaded = 0;
- load_msrs(vmx->host_msrs + vmx->msr_offset_efer, 1);
- }
+ vmx->guest_msrs[efer_offset].data = guest_efer;
+ return true;
}

static void vmx_save_host_state(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
+ int i;

if (vmx->host_state.loaded)
return;
@@ -655,8 +634,8 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
}
#endif
- load_msrs(vmx->guest_msrs, vmx->save_nmsrs);
- load_transition_efer(vmx);
+ for (i = 0; i < vmx->save_nmsrs; ++i)
+ kvm_set_shared_msr(i, vmx->guest_msrs[i].data);
}

static void __vmx_load_host_state(struct vcpu_vmx *vmx)
@@ -684,9 +663,6 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
local_irq_restore(flags);
}
reload_tss();
- save_msrs(vmx->guest_msrs, vmx->save_nmsrs);
- load_msrs(vmx->host_msrs, vmx->save_nmsrs);
- reload_host_efer(vmx);
#ifdef CONFIG_X86_64
if (is_long_mode(&vmx->vcpu)) {
rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
@@ -886,14 +862,11 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
#ifdef CONFIG_X86_64
static void move_msr_up(struct vcpu_vmx *vmx, int from, int to)
{
- struct kvm_msr_entry tmp;
+ struct shared_msr_entry tmp;

tmp = vmx->guest_msrs[to];
vmx->guest_msrs[to] = vmx->guest_msrs[from];
vmx->guest_msrs[from] = tmp;
- tmp = vmx->host_msrs[to];
- vmx->host_msrs[to] = vmx->host_msrs[from];
- vmx->host_msrs[from] = tmp;
}
#endif

@@ -904,15 +877,13 @@ static void move_msr_up(struct vcpu_vmx *vmx, int from, int to)
*/
static void setup_msrs(struct vcpu_vmx *vmx)
{
- int save_nmsrs;
+ int save_nmsrs, index;
unsigned long *msr_bitmap;

vmx_load_host_state(vmx);
save_nmsrs = 0;
#ifdef CONFIG_X86_64
if (is_long_mode(&vmx->vcpu)) {
- int index;
-
index = __find_msr_index(vmx, MSR_SYSCALL_MASK);
if (index >= 0)
move_msr_up(vmx, index, save_nmsrs++);
@@ -931,9 +902,11 @@ static void setup_msrs(struct vcpu_vmx *vmx)
move_msr_up(vmx, index, save_nmsrs++);
}
#endif
- vmx->save_nmsrs = save_nmsrs;
+ vmx->msr_offset_efer = index = __find_msr_index(vmx, MSR_EFER);
+ if (index >= 0 && update_transition_efer(vmx))
+ move_msr_up(vmx, index, save_nmsrs++);

- vmx->msr_offset_efer = __find_msr_index(vmx, MSR_EFER);
+ vmx->save_nmsrs = save_nmsrs;

if (cpu_has_vmx_msr_bitmap()) {
if (is_long_mode(&vmx->vcpu))
@@ -975,7 +948,7 @@ static void guest_write_tsc(u64 guest_tsc, u64 host_tsc)
static int vmx_get_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
{
u64 data;
- struct kvm_msr_entry *msr;
+ struct shared_msr_entry *msr;

if (!pdata) {
printk(KERN_ERR "BUG: get_msr called with NULL pdata\n");
@@ -994,9 +967,9 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
vmx_load_host_state(to_vmx(vcpu));
data = to_vmx(vcpu)->msr_guest_kernel_gs_base;
break;
+#endif
case MSR_EFER:
return kvm_get_msr_common(vcpu, msr_index, pdata);
-#endif
case MSR_IA32_TSC:
data = guest_read_tsc();
break;
@@ -1010,6 +983,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
data = vmcs_readl(GUEST_SYSENTER_ESP);
break;
default:
+ vmx_load_host_state(to_vmx(vcpu));
msr = find_msr_entry(to_vmx(vcpu), msr_index);
if (msr) {
vmx_load_host_state(to_vmx(vcpu));
@@ -1031,7 +1005,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- struct kvm_msr_entry *msr;
+ struct shared_msr_entry *msr;
u64 host_tsc;
int ret = 0;

@@ -1543,8 +1517,10 @@ continue_rmode:
static void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- struct kvm_msr_entry *msr = find_msr_entry(vmx, MSR_EFER);
+ struct shared_msr_entry *msr = find_msr_entry(vmx, MSR_EFER);

+ if (!msr)
+ return;
vcpu->arch.shadow_efer = efer;
if (!msr)
return;
@@ -2383,10 +2359,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
if (wrmsr_safe(index, data_low, data_high) < 0)
continue;
data = data_low | ((u64)data_high << 32);
- vmx->host_msrs[j].index = index;
- vmx->host_msrs[j].reserved = 0;
- vmx->host_msrs[j].data = data;
- vmx->guest_msrs[j] = vmx->host_msrs[j];
+ vmx->guest_msrs[j].index = i;
+ vmx->guest_msrs[j].data = 0;
++vmx->nmsrs;
}

@@ -3774,7 +3748,6 @@ static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
__clear_bit(vmx->vpid, vmx_vpid_bitmap);
spin_unlock(&vmx_vpid_lock);
vmx_free_vmcs(vcpu);
- kfree(vmx->host_msrs);
kfree(vmx->guest_msrs);
kvm_vcpu_uninit(vcpu);
kmem_cache_free(kvm_vcpu_cache, vmx);
@@ -3801,10 +3774,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
goto uninit_vcpu;
}

- vmx->host_msrs = kmalloc(PAGE_SIZE, GFP_KERNEL);
- if (!vmx->host_msrs)
- goto free_guest_msrs;
-
vmx->vmcs = alloc_vmcs();
if (!vmx->vmcs)
goto free_msrs;
@@ -3835,8 +3804,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
free_vmcs:
free_vmcs(vmx->vmcs);
free_msrs:
- kfree(vmx->host_msrs);
-free_guest_msrs:
kfree(vmx->guest_msrs);
uninit_vcpu:
kvm_vcpu_uninit(&vmx->vcpu);
@@ -3986,7 +3953,12 @@ static struct kvm_x86_ops vmx_x86_ops = {

static int __init vmx_init(void)
{
- int r;
+ int r, i;
+
+ rdmsrl_safe(MSR_EFER, &host_efer);
+
+ for (i = 0; i < NR_VMX_MSR; ++i)
+ kvm_define_shared_msr(i, vmx_msr_index[i]);

vmx_io_bitmap_a = (unsigned long *)__get_free_page(GFP_KERNEL);
if (!vmx_io_bitmap_a)
--
1.6.4.1