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, 9 insertions, 16 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index dbcdb55094f..d11be3fb7c8 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -66,7 +66,7 @@ module_param(emulate_invalid_guest_state, bool, S_IRUGO);
 #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 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
 {
 	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 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
 		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_activate(struct kvm_vcpu *vcpu)
 
 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 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	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 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	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 @@ static void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 
 	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 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 		};
 		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 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.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,