KVM: VMX: Add lazy FPU support for VT

Only save/restore the FPU host state when the guest is actually using the
FPU.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 56 insertions, 5 deletions

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 09608114e29a..5a2a68dec6bf 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -101,6 +101,13 @@ static inline int is_page_fault(u32 intr_info)
                 (INTR_TYPE_EXCEPTION | PF_VECTOR | INTR_INFO_VALID_MASK);
 }
 
+static inline int is_no_device(u32 intr_info)
+{
+        return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK |
+                             INTR_INFO_VALID_MASK)) ==
+                (INTR_TYPE_EXCEPTION | NM_VECTOR | INTR_INFO_VALID_MASK);
+}
+
 static inline int is_external_interrupt(u32 intr_info)
 {
         return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VALID_MASK))
@@ -216,6 +223,16 @@ static void vmcs_write64(unsigned long field, u64 value)
 #endif
 }
 
+static void vmcs_clear_bits(unsigned long field, u32 mask)
+{
+        vmcs_writel(field, vmcs_readl(field) & ~mask);
+}
+
+static void vmcs_set_bits(unsigned long field, u32 mask)
+{
+        vmcs_writel(field, vmcs_readl(field) | mask);
+}
+
 /*
  * Switches to specified vcpu, until a matching vcpu_put(), but assumes
  * vcpu mutex is already taken.
@@ -833,6 +850,11 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
         }
 #endif
 
+        if (!(cr0 & CR0_TS_MASK)) {
+                vcpu->fpu_active = 1;
+                vmcs_clear_bits(EXCEPTION_BITMAP, CR0_TS_MASK);
+        }
+
         vmcs_writel(CR0_READ_SHADOW, cr0);
         vmcs_writel(GUEST_CR0,
                     (cr0 & ~KVM_GUEST_CR0_MASK) | KVM_VM_CR0_ALWAYS_ON);
@@ -842,6 +864,12 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 static void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 {
         vmcs_writel(GUEST_CR3, cr3);
+
+        if (!(vcpu->cr0 & CR0_TS_MASK)) {
+                vcpu->fpu_active = 0;
+                vmcs_set_bits(GUEST_CR0, CR0_TS_MASK);
+                vmcs_set_bits(EXCEPTION_BITMAP, 1 << NM_VECTOR);
+        }
 }
 
 static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
@@ -1368,6 +1396,15 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                 asm ("int $2");
                 return 1;
         }
+
+        if (is_no_device(intr_info)) {
+                vcpu->fpu_active = 1;
+                vmcs_clear_bits(EXCEPTION_BITMAP, 1 << NM_VECTOR);
+                if (!(vcpu->cr0 & CR0_TS_MASK))
+                        vmcs_clear_bits(GUEST_CR0, CR0_TS_MASK);
+                return 1;
+        }
+
         error_code = 0;
         rip = vmcs_readl(GUEST_RIP);
         if (intr_info & INTR_INFO_DELIEVER_CODE_MASK)
@@ -1556,7 +1593,11 @@ static int handle_cr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                 break;
         case 2: /* clts */
                 vcpu_load_rsp_rip(vcpu);
-                set_cr0(vcpu, vcpu->cr0 & ~CR0_TS_MASK);
+                vcpu->fpu_active = 1;
+                vmcs_clear_bits(EXCEPTION_BITMAP, 1 << NM_VECTOR);
+                vmcs_clear_bits(GUEST_CR0, CR0_TS_MASK);
+                vcpu->cr0 &= ~CR0_TS_MASK;
+                vmcs_writel(CR0_READ_SHADOW, vcpu->cr0);
                 skip_emulated_instruction(vcpu);
                 return 1;
         case 1: /*mov from cr*/
@@ -1806,8 +1847,14 @@ again:
         if (vcpu->guest_debug.enabled)
                 kvm_guest_debug_pre(vcpu);
 
-        fx_save(vcpu->host_fx_image);
-        fx_restore(vcpu->guest_fx_image);
+        if (vcpu->fpu_active) {
+                fx_save(vcpu->host_fx_image);
+                fx_restore(vcpu->guest_fx_image);
+        }
+        /*
+         * Loading guest fpu may have cleared host cr0.ts
+         */
+        vmcs_writel(HOST_CR0, read_cr0());
 
 #ifdef CONFIG_X86_64
         if (is_long_mode(vcpu)) {
@@ -1965,8 +2012,11 @@ again:
         }
 #endif
 
-        fx_save(vcpu->guest_fx_image);
-        fx_restore(vcpu->host_fx_image);
+        if (vcpu->fpu_active) {
+                fx_save(vcpu->guest_fx_image);
+                fx_restore(vcpu->host_fx_image);
+        }
+
         vcpu->interrupt_window_open = (vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & 3) == 0;
 
         asm ("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));
@@ -2078,6 +2128,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
         vmcs_clear(vmcs);
         vcpu->vmcs = vmcs;
         vcpu->launched = 0;
+        vcpu->fpu_active = 1;
 
         return 0;