KVM: VMX: Avoid vmwrite(HOST_RSP) when possible
Usually HOST_RSP retains its value across guest entries. Take advantage
of this and avoid a vmwrite() when this is so.
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fc8996b..ddb49e3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -58,6 +58,7 @@
struct vcpu_vmx {
struct kvm_vcpu vcpu;
struct list_head local_vcpus_link;
+ unsigned long host_rsp;
int launched;
u8 fail;
u32 idt_vectoring_info;
@@ -2982,7 +2983,11 @@
/* Store host registers */
"push %%"R"dx; push %%"R"bp;"
"push %%"R"cx \n\t"
+ "cmp %%"R"sp, %c[host_rsp](%0) \n\t"
+ "je 1f \n\t"
+ "mov %%"R"sp, %c[host_rsp](%0) \n\t"
__ex(ASM_VMX_VMWRITE_RSP_RDX) "\n\t"
+ "1: \n\t"
/* Check if vmlaunch of vmresume is needed */
"cmpl $0, %c[launched](%0) \n\t"
/* Load guest registers. Don't clobber flags. */
@@ -3039,6 +3044,7 @@
: : "c"(vmx), "d"((unsigned long)HOST_RSP),
[launched]"i"(offsetof(struct vcpu_vmx, launched)),
[fail]"i"(offsetof(struct vcpu_vmx, fail)),
+ [host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)),
[rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])),
[rbx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBX])),
[rcx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RCX])),