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 c65ff62e11f506dd64749a7e5b2a1d56c83ebd45..56c46a50d85a60cd25a38886014083b394e2e171 100644 (file)
--- 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 */