On Fri, Jan 20, 2023, Alexey Kardashevskiy wrote: > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index 4826e6cc611b..61f2cad1cbaf 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -389,6 +389,8 @@ static inline bool vmcb12_is_intercept(struct vmcb_ctrl_area_cached *control, u3 > return test_bit(bit, (unsigned long *)&control->intercepts); > } > > +extern bool sev_es_is_debug_swap_enabled(void); > + > static inline void set_dr_intercepts(struct vcpu_svm *svm) > { > struct vmcb *vmcb = svm->vmcb01.ptr; > @@ -410,8 +412,10 @@ static inline void set_dr_intercepts(struct vcpu_svm *svm) > vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE); > } > > - vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ); > - vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE); > + if (!sev_es_guest(svm->vcpu.kvm) || !sev_es_is_debug_swap_enabled()) { Looking below, doesn't this do the wrong thing if set_dr_intercepts() is called before SVM_SEV_FEAT_DEBUG_SWAP is set? I.e. when this is called before LAUNCH_UPDATE? Seems like this should check SVM_SEV_FEAT_DEBUG_SWAP in sev_features regardless of when SVM_SEV_FEAT_DEBUG_SWAP is set. And if KVM checks sev_features, then I _think_ we can avoid having to expose sev_es_debug_swap_enabled to svm.{c,h} (though why on earth {set,clr}_dr_intercepts() is in svm.h is another question for the future). Follow-up question: does KVM _have_ to wait until KVM_SEV_LAUNCH_UPDATE_VMSA to set the flag? > + vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ); > + vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE); > + } > > recalc_intercepts(svm); > } > @@ -422,8 +426,12 @@ static inline void clr_dr_intercepts(struct vcpu_svm *svm) > > vmcb->control.intercepts[INTERCEPT_DR] = 0; > > - /* DR7 access must remain intercepted for an SEV-ES guest */ > - if (sev_es_guest(svm->vcpu.kvm)) { > + /* > + * DR7 access must remain intercepted for an SEV-ES guest unless DebugSwap > + * (depends on NO_NESTED_DATA_BP) is enabled as otherwise a VM writing to DR7 > + * from the #DB handler may trigger infinite loop of #DB's. > + */ > + if (sev_es_guest(svm->vcpu.kvm) && !sev_es_is_debug_swap_enabled()) { > vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ); > vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE); > } > > @@ -52,11 +53,21 @@ module_param_named(sev, sev_enabled, bool, 0444); > /* enable/disable SEV-ES support */ > static bool sev_es_enabled = true; > module_param_named(sev_es, sev_es_enabled, bool, 0444); > + > +/* enable/disable SEV-ES DebugSwap support */ > +static bool sev_es_debug_swap_enabled = true; > +module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0644); Module param needs 0444 permissions, i.e. shouldn't be writable after KVM is loaded. Though I don't know that providing a module param is warranted in this case. KVM provides module params for SEV and SEV-ES because there are legitimate reasons to turn them off, but at a glance, I don't see why we'd want that for this feature. > #else > #define sev_enabled false > #define sev_es_enabled false > +#define sev_es_debug_swap false This needs to be sev_es_debug_swap_enabled, otherwise things fall apart with CONFIG_KVM_AMD_SEV=n. arch/x86/kvm/svm/sev.c: In function ‘sev_es_is_debug_swap_enabled’: arch/x86/kvm/svm/sev.c:69:16: error: ‘sev_es_debug_swap_enabled’ undeclared (first use in this function); did you mean ‘sev_es_is_debug_swap_enabled’? 69 | return sev_es_debug_swap_enabled; | ^~~~~~~~~~~~~~~~~~~~~~~~~ | sev_es_is_debug_swap_enabled > #endif /* CONFIG_KVM_AMD_SEV */ > > +bool sev_es_is_debug_swap_enabled(void) > +{ > + return sev_es_debug_swap_enabled; > +} ... > @@ -604,6 +615,9 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm) > save->xss = svm->vcpu.arch.ia32_xss; > save->dr6 = svm->vcpu.arch.dr6; > > + if (sev_es_is_debug_swap_enabled()) > + save->sev_features |= SVM_SEV_FEAT_DEBUG_SWAP; > + > pr_debug("Virtual Machine Save Area (VMSA):\n"); > print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, save, sizeof(*save), false); > > @@ -2249,6 +2263,9 @@ void __init sev_hardware_setup(void) > out: > sev_enabled = sev_supported; > sev_es_enabled = sev_es_supported; > + if (sev_es_debug_swap_enabled) > + sev_es_debug_swap_enabled = sev_es_enabled && > + cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP); Slight preference for: if (!sev_es_enabled || !cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP)) sev_es_debug_swap_enabled = false; KVM does short-circuit some checks on module param values, but usually only to avoid additional setup. > #endif > } > > @@ -3027,6 +3044,18 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa) > > /* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */ > hostsa->xss = host_xss; > + > + /* The DebugSwap SEV feature does Type B swaps of DR[0-3] */ > + if (sev_es_is_debug_swap_enabled()) { > + hostsa->dr0 = native_get_debugreg(0); > + hostsa->dr1 = native_get_debugreg(1); > + hostsa->dr2 = native_get_debugreg(2); > + hostsa->dr3 = native_get_debugreg(3); > + hostsa->dr0_addr_mask = amd_get_dr_addr_mask(0); > + hostsa->dr1_addr_mask = amd_get_dr_addr_mask(1); > + hostsa->dr2_addr_mask = amd_get_dr_addr_mask(2); > + hostsa->dr3_addr_mask = amd_get_dr_addr_mask(3); > + } > } > > void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector) > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 60c7c880266b..6c54a3c9d442 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -1190,7 +1190,8 @@ static void init_vmcb(struct kvm_vcpu *vcpu) > set_exception_intercept(svm, UD_VECTOR); > set_exception_intercept(svm, MC_VECTOR); > set_exception_intercept(svm, AC_VECTOR); > - set_exception_intercept(svm, DB_VECTOR); > + if (!sev_es_is_debug_swap_enabled()) > + set_exception_intercept(svm, DB_VECTOR); This is wrong. KVM needs to intercept #DBs when debugging non-SEV-ES VMs. This _could_ be tied to X86_FEATURE_NO_NESTED_DATA_BP, but the KVM would need to toggle the intercept depending on whether or not userspace wants to debug the guest. Similar to the DR7 interception, can this check sev_features directly?