| Message ID | 20231108183003.5981-10-xin3.li@intel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Enable FRED with KVM VMX | expand |
On Wed, Nov 08, 2023 at 10:29:49AM -0800, Xin Li wrote: >Switch MSR_IA32_FRED_RSP0 between host and guest in >vmx_prepare_switch_to_{host,guest}(). > >MSR_IA32_FRED_RSP0 is used during ring 3 event delivery only, thus >KVM, running on ring 0, can run safely with guest FRED RSP0, i.e., >no need to switch between host/guest FRED RSP0 during VM entry and >exit. > >KVM should switch to host FRED RSP0 before returning to user level, >and switch to guest FRED RSP0 before entering guest mode. > >Tested-by: Shan Kang <shan.kang@intel.com> >Signed-off-by: Xin Li <xin3.li@intel.com> >--- > arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++++++ > arch/x86/kvm/vmx/vmx.h | 2 ++ > 2 files changed, 19 insertions(+) > >diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >index 41772ecdd368..d00ab9d4c93e 100644 >--- a/arch/x86/kvm/vmx/vmx.c >+++ b/arch/x86/kvm/vmx/vmx.c >@@ -1344,6 +1344,17 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > } > > wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base); >+ >+ if (cpu_feature_enabled(X86_FEATURE_FRED) && >+ guest_cpuid_has(vcpu, X86_FEATURE_FRED)) { >+ /* >+ * MSR_IA32_FRED_RSP0 is top of task stack, which never changes. >+ * Thus it should be initialized only once. >+ */ >+ if (unlikely(vmx->msr_host_fred_rsp0 == 0)) >+ vmx->msr_host_fred_rsp0 = read_msr(MSR_IA32_FRED_RSP0); >+ wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_guest_fred_rsp0); >+ } > #else > savesegment(fs, fs_sel); > savesegment(gs, gs_sel); >@@ -1388,6 +1399,12 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx) > invalidate_tss_limit(); > #ifdef CONFIG_X86_64 > wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base); >+ >+ if (cpu_feature_enabled(X86_FEATURE_FRED) && >+ guest_cpuid_has(&vmx->vcpu, X86_FEATURE_FRED)) { IIUC, vmx_prepare_switch_to_host() is called from IRQ-disabled context. using guest_cpuid_has() in this context is not desired, see lockdep_assert_irqs_enabled() in cpuid_entry2_find(). >+ vmx->msr_guest_fred_rsp0 = read_msr(MSR_IA32_FRED_RSP0); >+ wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_host_fred_rsp0); >+ } > #endif > load_fixmap_gdt(raw_smp_processor_id()); > vmx->guest_state_loaded = false; >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h >index f8c02bd37069..328a3447f064 100644 >--- a/arch/x86/kvm/vmx/vmx.h >+++ b/arch/x86/kvm/vmx/vmx.h >@@ -276,6 +276,8 @@ struct vcpu_vmx { > #ifdef CONFIG_X86_64 > u64 msr_host_kernel_gs_base; > u64 msr_guest_kernel_gs_base; >+ u64 msr_host_fred_rsp0; >+ u64 msr_guest_fred_rsp0; resetting guest fred rsp0 to 0 during vcpu reset is missing. > #endif > > u64 spec_ctrl; >-- >2.42.0 > >
> >+ if (cpu_feature_enabled(X86_FEATURE_FRED) && > >+ guest_cpuid_has(&vmx->vcpu, X86_FEATURE_FRED)) { > > IIUC, vmx_prepare_switch_to_host() is called from IRQ-disabled context. using > guest_cpuid_has() in this context is not desired, see > lockdep_assert_irqs_enabled() in cpuid_entry2_find(). Nice catch! Anyway it's a bad idea to do a search call here, let me find a better way for all FRED CPUID checks. > >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index > >f8c02bd37069..328a3447f064 100644 > >--- a/arch/x86/kvm/vmx/vmx.h > >+++ b/arch/x86/kvm/vmx/vmx.h > >@@ -276,6 +276,8 @@ struct vcpu_vmx { > > #ifdef CONFIG_X86_64 > > u64 msr_host_kernel_gs_base; > > u64 msr_guest_kernel_gs_base; > >+ u64 msr_host_fred_rsp0; > >+ u64 msr_guest_fred_rsp0; > > resetting guest fred rsp0 to 0 during vcpu reset is missing. hmm, I assume it gets the same treatment as guest_kernel_gs_base. It seems we don't reset guest_kernel_gs_base. No?
>> >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index >> >f8c02bd37069..328a3447f064 100644 >> >--- a/arch/x86/kvm/vmx/vmx.h >> >+++ b/arch/x86/kvm/vmx/vmx.h >> >@@ -276,6 +276,8 @@ struct vcpu_vmx { >> > #ifdef CONFIG_X86_64 >> > u64 msr_host_kernel_gs_base; >> > u64 msr_guest_kernel_gs_base; >> >+ u64 msr_host_fred_rsp0; >> >+ u64 msr_guest_fred_rsp0; >> >> resetting guest fred rsp0 to 0 during vcpu reset is missing. > >hmm, I assume it gets the same treatment as guest_kernel_gs_base. > >It seems we don't reset guest_kernel_gs_base. No? Yes. But for fred MSRs, FRED spec clearly says their RESET values are 0s. for kernel_gs_base MSR, looks there is no such description in SDM.
> >> >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index > >> >f8c02bd37069..328a3447f064 100644 > >> >--- a/arch/x86/kvm/vmx/vmx.h > >> >+++ b/arch/x86/kvm/vmx/vmx.h > >> >@@ -276,6 +276,8 @@ struct vcpu_vmx { > >> > #ifdef CONFIG_X86_64 > >> > u64 msr_host_kernel_gs_base; > >> > u64 msr_guest_kernel_gs_base; > >> >+ u64 msr_host_fred_rsp0; > >> >+ u64 msr_guest_fred_rsp0; > >> > >> resetting guest fred rsp0 to 0 during vcpu reset is missing. > > > >hmm, I assume it gets the same treatment as guest_kernel_gs_base. > > > >It seems we don't reset guest_kernel_gs_base. No? > > Yes. But for fred MSRs, FRED spec clearly says their RESET values > are 0s. for kernel_gs_base MSR, looks there is no such description > in SDM. Right, maybe better to set both to 0s.
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 41772ecdd368..d00ab9d4c93e 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1344,6 +1344,17 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) } wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base); + + if (cpu_feature_enabled(X86_FEATURE_FRED) && + guest_cpuid_has(vcpu, X86_FEATURE_FRED)) { + /* + * MSR_IA32_FRED_RSP0 is top of task stack, which never changes. + * Thus it should be initialized only once. + */ + if (unlikely(vmx->msr_host_fred_rsp0 == 0)) + vmx->msr_host_fred_rsp0 = read_msr(MSR_IA32_FRED_RSP0); + wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_guest_fred_rsp0); + } #else savesegment(fs, fs_sel); savesegment(gs, gs_sel); @@ -1388,6 +1399,12 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx) invalidate_tss_limit(); #ifdef CONFIG_X86_64 wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base); + + if (cpu_feature_enabled(X86_FEATURE_FRED) && + guest_cpuid_has(&vmx->vcpu, X86_FEATURE_FRED)) { + vmx->msr_guest_fred_rsp0 = read_msr(MSR_IA32_FRED_RSP0); + wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_host_fred_rsp0); + } #endif load_fixmap_gdt(raw_smp_processor_id()); vmx->guest_state_loaded = false; diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index f8c02bd37069..328a3447f064 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -276,6 +276,8 @@ struct vcpu_vmx { #ifdef CONFIG_X86_64 u64 msr_host_kernel_gs_base; u64 msr_guest_kernel_gs_base; + u64 msr_host_fred_rsp0; + u64 msr_guest_fred_rsp0; #endif u64 spec_ctrl;
Switch MSR_IA32_FRED_RSP0 between host and guest in vmx_prepare_switch_to_{host,guest}(). MSR_IA32_FRED_RSP0 is used during ring 3 event delivery only, thus KVM, running on ring 0, can run safely with guest FRED RSP0, i.e., no need to switch between host/guest FRED RSP0 during VM entry and exit. KVM should switch to host FRED RSP0 before returning to user level, and switch to guest FRED RSP0 before entering guest mode. Tested-by: Shan Kang <shan.kang@intel.com> Signed-off-by: Xin Li <xin3.li@intel.com> --- arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++++++ arch/x86/kvm/vmx/vmx.h | 2 ++ 2 files changed, 19 insertions(+)