KVM: VMX: Avoid writing HOST_CR0 every entry

cr0.ts may change between entries, so we copy cr0 to HOST_CR0 before each
entry.  That is slow, so instead, set HOST_CR0 to have TS set unconditionally
(which is a safe value), and issue a clts() just before exiting vcpu context
if the task indeed owns the fpu.

Saves ~50 cycles/exit.

Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 3 insertions, 6 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 64252075796a..598931734251 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -812,6 +812,8 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
                 wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
         }
 #endif
+        if (current_thread_info()->status & TS_USEDFPU)
+                clts();
 }
 
 static void vmx_load_host_state(struct vcpu_vmx *vmx)
@@ -2507,7 +2509,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
         vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, !!bypass_guest_pf);
         vmcs_write32(CR3_TARGET_COUNT, 0);           /* 22.2.1 */
 
-        vmcs_writel(HOST_CR0, read_cr0());  /* 22.2.3 */
+        vmcs_writel(HOST_CR0, read_cr0() | X86_CR0_TS);  /* 22.2.3 */
         vmcs_writel(HOST_CR4, read_cr4());  /* 22.2.3, 22.2.5 */
         vmcs_writel(HOST_CR3, read_cr3());  /* 22.2.3  FIXME: shadow tables */
 
@@ -3859,11 +3861,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
         if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
                 vmx_set_interrupt_shadow(vcpu, 0);
 
-        /*
-         * Loading guest fpu may have cleared host cr0.ts
-         */
-        vmcs_writel(HOST_CR0, read_cr0());
-
         asm(
                 /* Store host registers */
                 "push %%"R"dx; push %%"R"bp;"