Messages in this thread | | | Date | Thu, 18 Nov 2021 12:18:39 +0100 | Subject | Re: [PATCH 02/15] KVM: VMX: Avoid to rdmsrl(MSR_IA32_SYSENTER_ESP) | From | Paolo Bonzini <> |
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On 11/18/21 12:08, Lai Jiangshan wrote: > From: Lai Jiangshan <laijs@linux.alibaba.com> > > 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>
Then it's not constant host state, isn't? The hunk in vmx_set_constant_host_state seems wrong.
Paolo
> --- > arch/x86/kvm/vmx/vmx.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 48a34d1a2989..4e4a33226edb 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; > } > @@ -4021,6 +4023,8 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx) > > rdmsr(MSR_IA32_SYSENTER_CS, low32, high32); > vmcs_write32(HOST_IA32_SYSENTER_CS, low32); > + rdmsrl(MSR_IA32_SYSENTER_ESP, tmpl); > + vmcs_writel(HOST_IA32_SYSENTER_ESP, tmpl); > rdmsrl(MSR_IA32_SYSENTER_EIP, tmpl); > vmcs_writel(HOST_IA32_SYSENTER_EIP, tmpl); /* 22.2.3 */
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