Messages in this thread | | | Date | Sun, 7 Apr 2024 11:02:52 +0800 | Subject | Re: [PATCH v19 079/130] KVM: TDX: vcpu_run: save/restore host state(host kernel gs) | From | Binbin Wu <> |
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On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote: > From: Isaku Yamahata <isaku.yamahata@intel.com> > > On entering/exiting TDX vcpu, Preserved or clobbered CPU state is different > from VMX case.
Could you add more descriptions about the differences?
> Add TDX hooks to save/restore host/guest CPU state.
KVM doesn't save/restore guest CPU state for TDX.
> Save/restore kernel GS base MSR. > > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> > --- > arch/x86/kvm/vmx/main.c | 30 +++++++++++++++++++++++++-- > arch/x86/kvm/vmx/tdx.c | 42 ++++++++++++++++++++++++++++++++++++++ > arch/x86/kvm/vmx/tdx.h | 4 ++++ > arch/x86/kvm/vmx/x86_ops.h | 4 ++++ > 4 files changed, 78 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c > index d72651ce99ac..8275a242ce07 100644 > --- a/arch/x86/kvm/vmx/main.c > +++ b/arch/x86/kvm/vmx/main.c > @@ -158,6 +158,32 @@ static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) > vmx_vcpu_reset(vcpu, init_event); > } > > +static void vt_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > +{ > + /* > + * All host state is saved/restored across SEAMCALL/SEAMRET,
It sounds confusing to me. If all host states are saved/restored across SEAMCALL/SEAMRET, why this patch saves/restores MSR_KERNEL_GS_BASE for host?
> and the > + * guest state of a TD is obviously off limits. Deferring MSRs and DRs > + * is pointless because the TDX module needs to load *something* so as > + * not to expose guest state. > + */ > + if (is_td_vcpu(vcpu)) { > + tdx_prepare_switch_to_guest(vcpu); > + return; > + } > + > + vmx_prepare_switch_to_guest(vcpu); > +} > + > +static void vt_vcpu_put(struct kvm_vcpu *vcpu) > +{ > + if (is_td_vcpu(vcpu)) { > + tdx_vcpu_put(vcpu); > + return; > + } > + > + vmx_vcpu_put(vcpu); > +} > + > static int vt_vcpu_pre_run(struct kvm_vcpu *vcpu) > { > if (is_td_vcpu(vcpu)) > @@ -326,9 +352,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = { > .vcpu_free = vt_vcpu_free, > .vcpu_reset = vt_vcpu_reset, > > - .prepare_switch_to_guest = vmx_prepare_switch_to_guest, > + .prepare_switch_to_guest = vt_prepare_switch_to_guest, > .vcpu_load = vmx_vcpu_load, > - .vcpu_put = vmx_vcpu_put, > + .vcpu_put = vt_vcpu_put, > > .update_exception_bitmap = vmx_update_exception_bitmap, > .get_msr_feature = vmx_get_msr_feature, > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index fdf9196cb592..9616b1aab6ce 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -1,5 +1,6 @@ > // SPDX-License-Identifier: GPL-2.0 > #include <linux/cpu.h> > +#include <linux/mmu_context.h> > > #include <asm/tdx.h> > > @@ -423,6 +424,7 @@ u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) > int tdx_vcpu_create(struct kvm_vcpu *vcpu) > { > struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm); > + struct vcpu_tdx *tdx = to_tdx(vcpu); > > WARN_ON_ONCE(vcpu->arch.cpuid_entries); > WARN_ON_ONCE(vcpu->arch.cpuid_nent); > @@ -446,9 +448,47 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu) > if ((kvm_tdx->xfam & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE) > vcpu->arch.xfd_no_write_intercept = true; > > + tdx->host_state_need_save = true; > + tdx->host_state_need_restore = false; > + > return 0; > } > > +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
Just like vmx_prepare_switch_to_host(), the input can be "struct vcpu_tdx *", since vcpu is not used inside the function. And the callsites just use "to_tdx(vcpu)"
> +{ > + struct vcpu_tdx *tdx = to_tdx(vcpu); Then, this can be dropped.
> + > + if (!tdx->host_state_need_save) > + return; > + > + if (likely(is_64bit_mm(current->mm))) > + tdx->msr_host_kernel_gs_base = current->thread.gsbase; > + else > + tdx->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE); > + > + tdx->host_state_need_save = false; > +} > + > +static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
ditto
> +{ > + struct vcpu_tdx *tdx = to_tdx(vcpu); > + > + tdx->host_state_need_save = true; > + if (!tdx->host_state_need_restore) > + return; > + > + ++vcpu->stat.host_state_reload; > + > + wrmsrl(MSR_KERNEL_GS_BASE, tdx->msr_host_kernel_gs_base); > + tdx->host_state_need_restore = false; > +} > + > +void tdx_vcpu_put(struct kvm_vcpu *vcpu) > +{ > + vmx_vcpu_pi_put(vcpu); > + tdx_prepare_switch_to_host(vcpu); > +} > + > void tdx_vcpu_free(struct kvm_vcpu *vcpu) > { > struct vcpu_tdx *tdx = to_tdx(vcpu); > @@ -569,6 +609,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) > > tdx_vcpu_enter_exit(tdx); > > + tdx->host_state_need_restore = true; > + > vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET; > trace_kvm_exit(vcpu, KVM_ISA_VMX); > > diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h > index 81d301fbe638..e96c416e73bf 100644 > --- a/arch/x86/kvm/vmx/tdx.h > +++ b/arch/x86/kvm/vmx/tdx.h > @@ -69,6 +69,10 @@ struct vcpu_tdx { > > bool initialized; > > + bool host_state_need_save; > + bool host_state_need_restore; > + u64 msr_host_kernel_gs_base; > + > /* > * Dummy to make pmu_intel not corrupt memory. > * TODO: Support PMU for TDX. Future work. > diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h > index 3e29a6fe28ef..9fd997c79c33 100644 > --- a/arch/x86/kvm/vmx/x86_ops.h > +++ b/arch/x86/kvm/vmx/x86_ops.h > @@ -151,6 +151,8 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu); > void tdx_vcpu_free(struct kvm_vcpu *vcpu); > void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event); > fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu); > +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu); > +void tdx_vcpu_put(struct kvm_vcpu *vcpu); > u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio); > > int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp); > @@ -186,6 +188,8 @@ static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; } > static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {} > static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {} > static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) { return EXIT_FASTPATH_NONE; } > +static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {} > +static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {} > static inline u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) { return 0; } > > static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
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