KVM: VMX: Avoid to rdmsrl(MSR_IA32_SYSENTER_ESP)
The value of host MSR_IA32_SYSENTER_ESP is known to be constant for
each CPU: (cpu_entry_stack(cpu) + 1) when 32 bit syscall is enabled or
NULL is 32 bit syscall is not enabled.
So rdmsrl() can be avoided for the first case and both rdmsrl() and
vmcs_writel() can be avoided for the second case.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211118110814.2568-3-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c65ff62..56c46a5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1271,7 +1271,6 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu,
if (!already_loaded) {
void *gdt = get_current_gdt_ro();
- unsigned long sysenter_esp;
/*
* Flush all EPTP/VPID contexts, the new pCPU may have stale
@@ -1287,8 +1286,11 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu,
(unsigned long)&get_cpu_entry_area(cpu)->tss.x86_tss);
vmcs_writel(HOST_GDTR_BASE, (unsigned long)gdt); /* 22.2.4 */
- rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
- vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
+ if (IS_ENABLED(CONFIG_IA32_EMULATION) || IS_ENABLED(CONFIG_X86_32)) {
+ /* 22.2.3 */
+ vmcs_writel(HOST_IA32_SYSENTER_ESP,
+ (unsigned long)(cpu_entry_stack(cpu) + 1));
+ }
vmx->loaded_vmcs->cpu = cpu;
}
@@ -4026,6 +4028,12 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
rdmsr(MSR_IA32_SYSENTER_CS, low32, high32);
vmcs_write32(HOST_IA32_SYSENTER_CS, low32);
+
+ /*
+ * If 32-bit syscall is enabled, vmx_vcpu_load_vcms rewrites
+ * HOST_IA32_SYSENTER_ESP.
+ */
+ vmcs_writel(HOST_IA32_SYSENTER_ESP, 0);
rdmsrl(MSR_IA32_SYSENTER_EIP, tmpl);
vmcs_writel(HOST_IA32_SYSENTER_EIP, tmpl); /* 22.2.3 */