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>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 6425207..5989317 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -812,6 +812,8 @@
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 @@
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 @@
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;"