KVM: Lazify fpu activation and deactivation
Defer fpu deactivation as much as possible - if the guest fpu is loaded, keep
it loaded until the next heavyweight exit (where we are forced to unload it).
This reduces unnecessary exits.
We also defer fpu activation on clts; while clts signals the intent to use the
fpu, we can't be sure the guest will actually use it.
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 693046a..93bee7a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -506,6 +506,7 @@
void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
void (*set_rflags)(struct kvm_vcpu *vcpu, unsigned long rflags);
+ void (*fpu_deactivate)(struct kvm_vcpu *vcpu);
void (*tlb_flush)(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3899c2d..5b336a8 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -984,17 +984,11 @@
if (npt_enabled)
goto set;
- if (kvm_read_cr0_bits(vcpu, X86_CR0_TS) && !(cr0 & X86_CR0_TS)) {
- svm->vmcb->control.intercept_exceptions &= ~(1 << NM_VECTOR);
- vcpu->fpu_active = 1;
- }
-
vcpu->arch.cr0 = cr0;
cr0 |= X86_CR0_PG | X86_CR0_WP;
- if (!vcpu->fpu_active) {
- svm->vmcb->control.intercept_exceptions |= (1 << NM_VECTOR);
+
+ if (!vcpu->fpu_active)
cr0 |= X86_CR0_TS;
- }
set:
/*
* re-enable caching here because the QEMU bios
@@ -1250,6 +1244,8 @@
svm->vmcb->control.intercept_exceptions &= ~(1 << NM_VECTOR);
if (!kvm_read_cr0_bits(&svm->vcpu, X86_CR0_TS))
svm->vmcb->save.cr0 &= ~X86_CR0_TS;
+ else
+ svm->vmcb->save.cr0 |= X86_CR0_TS;
svm->vcpu.fpu_active = 1;
return 1;
@@ -2586,6 +2582,8 @@
static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
{
+ if (npt_enabled)
+ vcpu->fpu_active = 1;
}
static inline void sync_cr8_to_lapic(struct kvm_vcpu *vcpu)
@@ -2805,12 +2803,6 @@
svm->vmcb->save.cr3 = root;
force_new_asid(vcpu);
-
- if (vcpu->fpu_active) {
- svm->vmcb->control.intercept_exceptions |= (1 << NM_VECTOR);
- svm->vmcb->save.cr0 |= X86_CR0_TS;
- vcpu->fpu_active = 0;
- }
}
static int is_disabled(void)
@@ -2926,6 +2918,20 @@
return false;
}
+static void svm_fpu_deactivate(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ if (npt_enabled) {
+ /* hack: npt requires active fpu at this time */
+ vcpu->fpu_active = 1;
+ return;
+ }
+
+ svm->vmcb->control.intercept_exceptions |= 1 << NM_VECTOR;
+ svm->vmcb->save.cr0 |= X86_CR0_TS;
+}
+
static struct kvm_x86_ops svm_x86_ops = {
.cpu_has_kvm_support = has_svm,
.disabled_by_bios = is_disabled,
@@ -2967,6 +2973,7 @@
.cache_reg = svm_cache_reg,
.get_rflags = svm_get_rflags,
.set_rflags = svm_set_rflags,
+ .fpu_deactivate = svm_fpu_deactivate,
.tlb_flush = svm_flush_tlb,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index dbcdb55..d11be3f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -66,7 +66,7 @@
#define KVM_GUEST_CR0_MASK \
(KVM_GUEST_CR0_MASK_UNRESTRICTED_GUEST | X86_CR0_PG | X86_CR0_PE)
#define KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST \
- (X86_CR0_WP | X86_CR0_NE | X86_CR0_TS | X86_CR0_MP)
+ (X86_CR0_WP | X86_CR0_NE | X86_CR0_MP)
#define KVM_VM_CR0_ALWAYS_ON \
(KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST | X86_CR0_PG | X86_CR0_PE)
#define KVM_CR4_GUEST_OWNED_BITS \
@@ -579,9 +579,8 @@
{
u32 eb;
- eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR);
- if (!vcpu->fpu_active)
- eb |= 1u << NM_VECTOR;
+ eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR)
+ | (1u << NM_VECTOR);
/*
* Unconditionally intercept #DB so we can maintain dr6 without
* reading it every exit.
@@ -595,6 +594,8 @@
eb = ~0;
if (enable_ept)
eb &= ~(1u << PF_VECTOR); /* bypass_guest_pf = 0 */
+ if (vcpu->fpu_active)
+ eb &= ~(1u << NM_VECTOR);
vmcs_write32(EXCEPTION_BITMAP, eb);
}
@@ -806,9 +807,6 @@
static void vmx_fpu_deactivate(struct kvm_vcpu *vcpu)
{
- if (!vcpu->fpu_active)
- return;
- vcpu->fpu_active = 0;
vmcs_set_bits(GUEST_CR0, X86_CR0_TS);
update_exception_bitmap(vcpu);
}
@@ -1737,8 +1735,6 @@
else
hw_cr0 = (cr0 & ~KVM_GUEST_CR0_MASK) | KVM_VM_CR0_ALWAYS_ON;
- vmx_fpu_deactivate(vcpu);
-
if (vmx->rmode.vm86_active && (cr0 & X86_CR0_PE))
enter_pmode(vcpu);
@@ -1757,12 +1753,12 @@
if (enable_ept)
ept_update_paging_mode_cr0(&hw_cr0, cr0, vcpu);
+ if (!vcpu->fpu_active)
+ hw_cr0 |= X86_CR0_TS;
+
vmcs_writel(CR0_READ_SHADOW, cr0);
vmcs_writel(GUEST_CR0, hw_cr0);
vcpu->arch.cr0 = cr0;
-
- if (!(cr0 & X86_CR0_TS) || !(cr0 & X86_CR0_PE))
- vmx_fpu_activate(vcpu);
}
static u64 construct_eptp(unsigned long root_hpa)
@@ -1793,8 +1789,6 @@
vmx_flush_tlb(vcpu);
vmcs_writel(GUEST_CR3, guest_cr3);
- if (kvm_read_cr0_bits(vcpu, X86_CR0_PE))
- vmx_fpu_deactivate(vcpu);
}
static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
@@ -3002,11 +2996,9 @@
};
break;
case 2: /* clts */
- vmx_fpu_deactivate(vcpu);
vcpu->arch.cr0 &= ~X86_CR0_TS;
vmcs_writel(CR0_READ_SHADOW, kvm_read_cr0(vcpu));
trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
- vmx_fpu_activate(vcpu);
skip_emulated_instruction(vcpu);
return 1;
case 1: /*mov from cr*/
@@ -4127,6 +4119,7 @@
.cache_reg = vmx_cache_reg,
.get_rflags = vmx_get_rflags,
.set_rflags = vmx_set_rflags,
+ .fpu_deactivate = vmx_fpu_deactivate,
.tlb_flush = vmx_flush_tlb,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 748b15d..1de2ad7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1509,8 +1509,8 @@
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
- kvm_x86_ops->vcpu_put(vcpu);
kvm_put_guest_fpu(vcpu);
+ kvm_x86_ops->vcpu_put(vcpu);
}
static int is_efer_nx(void)
@@ -4006,6 +4006,10 @@
r = 0;
goto out;
}
+ if (test_and_clear_bit(KVM_REQ_DEACTIVATE_FPU, &vcpu->requests)) {
+ vcpu->fpu_active = 0;
+ kvm_x86_ops->fpu_deactivate(vcpu);
+ }
}
preempt_disable();
@@ -5075,6 +5079,7 @@
kvm_fx_save(&vcpu->arch.guest_fx_image);
kvm_fx_restore(&vcpu->arch.host_fx_image);
++vcpu->stat.fpu_reload;
+ set_bit(KVM_REQ_DEACTIVATE_FPU, &vcpu->requests);
}
EXPORT_SYMBOL_GPL(kvm_put_guest_fpu);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index bb0314e..dfde04b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -38,6 +38,7 @@
#define KVM_REQ_MMU_SYNC 7
#define KVM_REQ_KVMCLOCK_UPDATE 8
#define KVM_REQ_KICK 9
+#define KVM_REQ_DEACTIVATE_FPU 10
#define KVM_USERSPACE_IRQ_SOURCE_ID 0