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>

1 files changed, 21 insertions, 14 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3899c2d19830..5b336a80f31e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -984,17 +984,11 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
         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 @@ static int nm_interception(struct vcpu_svm *svm)
         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_flush_tlb(struct kvm_vcpu *vcpu)
 
 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 @@ static void svm_set_cr3(struct kvm_vcpu *vcpu, unsigned long root)
 
         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 @@ static bool svm_rdtscp_supported(void)
         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 @@ static struct kvm_x86_ops svm_x86_ops = {
         .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,