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Subject[PATCH 24/40] KVM: VMX: Avoid vmwrite(HOST_RSP) when possible
Date
From: Avi Kivity <avi@qumranet.com>

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>
---
arch/x86/kvm/vmx.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)

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 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])),
--
1.6.0.1


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