| Message ID | 20240207172646.3981-10-xin3.li@intel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Enable FRED with KVM VMX | expand |
On Wed, Feb 07, 2024 at 09:26:29AM -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. > >Signed-off-by: Xin Li <xin3.li@intel.com> >Tested-by: Shan Kang <shan.kang@intel.com> >--- > >Changes since v1: >* Don't use guest_cpuid_has() in vmx_prepare_switch_to_{host,guest}(), > which are called from IRQ-disabled context (Chao Gao). >* Reset msr_guest_fred_rsp0 in __vmx_vcpu_reset() (Chao Gao). >--- > 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 b7b772183ee4..264378c3b784 100644 >--- a/arch/x86/kvm/vmx/vmx.c >+++ b/arch/x86/kvm/vmx/vmx.c >@@ -1337,6 +1337,16 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > } > > wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base); >+ >+ if (guest_can_use(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); can we just drop this and use "(unsigned long)task_stack_page(current) + THREAD_SIZE" as host fred rsp0? >+ wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_guest_fred_rsp0); any reason to not use wrmsrns? >+ } > #else > savesegment(fs, fs_sel); > savesegment(gs, gs_sel); >@@ -1381,6 +1391,11 @@ 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 (guest_can_use(&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); same question. >+ } > #endif > load_fixmap_gdt(raw_smp_processor_id()); > vmx->guest_state_loaded = false; >@@ -4889,6 +4904,8 @@ static void __vmx_vcpu_reset(struct kvm_vcpu *vcpu) > > #ifdef CONFIG_X86_64 > if (kvm_cpu_cap_has(X86_FEATURE_FRED)) { >+ vmx->msr_guest_fred_rsp0 = 0; >+ > vmcs_write64(GUEST_IA32_FRED_CONFIG, 0); > vmcs_write64(GUEST_IA32_FRED_RSP1, 0); > vmcs_write64(GUEST_IA32_FRED_RSP2, 0); >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h >index 3ad52437f426..176ad39be406 100644 >--- a/arch/x86/kvm/vmx/vmx.h >+++ b/arch/x86/kvm/vmx/vmx.h >@@ -278,6 +278,8 @@ 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; >-- >2.43.0 > >
> >+ if (unlikely(vmx->msr_host_fred_rsp0 == 0)) > >+ vmx->msr_host_fred_rsp0 = > read_msr(MSR_IA32_FRED_RSP0); > > can we just drop this and use "(unsigned long)task_stack_page(current) + > THREAD_SIZE" > as host fred rsp0? I thought about it, however, don't see a strong reason that it's better, i.e., is RDMSR slower than reading 'stack' from current task_struct? > > >+ wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_guest_fred_rsp0); > > any reason to not use wrmsrns? Good call! > >+ } > > #else > > savesegment(fs, fs_sel); > > savesegment(gs, gs_sel); > >@@ -1381,6 +1391,11 @@ 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 (guest_can_use(&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); > > same question. Will do! Thanks! Xin
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index b7b772183ee4..264378c3b784 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1337,6 +1337,16 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) } wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base); + + if (guest_can_use(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); @@ -1381,6 +1391,11 @@ 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 (guest_can_use(&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; @@ -4889,6 +4904,8 @@ static void __vmx_vcpu_reset(struct kvm_vcpu *vcpu) #ifdef CONFIG_X86_64 if (kvm_cpu_cap_has(X86_FEATURE_FRED)) { + vmx->msr_guest_fred_rsp0 = 0; + vmcs_write64(GUEST_IA32_FRED_CONFIG, 0); vmcs_write64(GUEST_IA32_FRED_RSP1, 0); vmcs_write64(GUEST_IA32_FRED_RSP2, 0); diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 3ad52437f426..176ad39be406 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -278,6 +278,8 @@ 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. Signed-off-by: Xin Li <xin3.li@intel.com> Tested-by: Shan Kang <shan.kang@intel.com> --- Changes since v1: * Don't use guest_cpuid_has() in vmx_prepare_switch_to_{host,guest}(), which are called from IRQ-disabled context (Chao Gao). * Reset msr_guest_fred_rsp0 in __vmx_vcpu_reset() (Chao Gao). --- arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++++++ arch/x86/kvm/vmx/vmx.h | 2 ++ 2 files changed, 19 insertions(+)