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KVM: VMX: Avoid to rdmsrl(MSR_IA32_SYSENTER_ESP)

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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>
This commit is contained in:
Lai Jiangshan 2021-11-18 19:08:01 +08:00 committed by Paolo Bonzini
parent 24cd19a28c
commit 6ab8a4053f
1 changed files with 11 additions and 3 deletions
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14
arch/x86/kvm/vmx/vmx.c
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@ -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 */