| Message ID | 20211118110814.2568-3-jiangshanlai@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: X86: Miscellaneous cleanups | expand |
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 */
On 2021/11/18 19:18, Paolo Bonzini wrote: > 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. > The change in vmx_vcpu_load_vmcs() handles only the percpu constant case: (cpu_entry_stack(cpu) + 1), it doesn't handle the case where MSR_IA32_SYSENTER_ESP is NULL. The change in vmx_set_constant_host_state() handles the case where MSR_IA32_SYSENTER_ESP is NULL, it does be constant host state in this case. If it is not the case, the added code in vmx_vcpu_load_vmcs() will override it safely. If an else branch with "vmcs_writel(HOST_IA32_SYSENTER_ESP, 0);" is added to vmx_vcpu_load_vmcs(), we will not need to change vmx_set_constant_host_state(). - 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)); + } else { + vmcs_writel(HOST_IA32_SYSENTER_ESP, 0); + } I'm paranoid about the case when vmcs.HOST_IA32_SYSENTER_ESP is not reset to be NULL when the vcpu is reset. So the hunk in vmx_set_constant_host_state() or the else branch in vmx_vcpu_load_vmcs() is required. I just chose to change the vmx_set_constant_host_state() so that we can reduce a vmcs_writel() in the case where CONFIG_IA32_EMULATION is off in x86_64. > 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 */ >
On 11/18/21 15:17, Lai Jiangshan wrote: > > The change in vmx_vcpu_load_vmcs() handles only the percpu constant case: > (cpu_entry_stack(cpu) + 1), it doesn't handle the case where > MSR_IA32_SYSENTER_ESP is NULL. > > The change in vmx_set_constant_host_state() handles the case where > MSR_IA32_SYSENTER_ESP is NULL, it does be constant host state in this case. > If it is not the case, the added code in vmx_vcpu_load_vmcs() will override > it safely. > > If an else branch with "vmcs_writel(HOST_IA32_SYSENTER_ESP, 0);" is > added to > vmx_vcpu_load_vmcs(), we will not need to change > vmx_set_constant_host_state(). We can change vmx_set_constant_host_state to write 0. Paolo
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 */