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/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,
