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>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fc8996b1043b..ddb49e34697b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -58,6 +58,7 @@ struct vmcs {
 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 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                 /* 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 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
               : : "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])),