From: Kevin Cheng Explicitly synthesize a #UD for VMMCALL if L2 is active, L1 does NOT want to intercept VMMCALL, nested_svm_l2_tlb_flush_enabled() is true, and the hypercall is something other than one of the supported Hyper-V hypercalls. When all of the above conditions are met, KVM will intercept VMMCALL but never forward it to L1, i.e. will let L2 make hypercalls as if it were L1. The TLFS says a whole lot of nothing about this scenario, so go with the architectural behavior, which says that VMMCALL #UDs if it's not intercepted. Opportunistically do a 2-for-1 stub trade by stub-ifying the new API instead of the helpers it uses. The last remaining "single" stub will soon be dropped as well. Suggested-by: Sean Christopherson Fixes: 3f4a812edf5c ("KVM: nSVM: hyper-v: Enable L2 TLB flush") Cc: Vitaly Kuznetsov Cc: stable@vger.kernel.org Signed-off-by: Kevin Cheng Link: https://patch.msgid.link/20260228033328.2285047-5-chengkev@google.com [sean: rewrite changelog and comment, tag for stable, remove defunct stubs] Signed-off-by: Sean Christopherson --- arch/x86/kvm/hyperv.h | 8 -------- arch/x86/kvm/svm/hyperv.h | 11 +++++++++++ arch/x86/kvm/svm/nested.c | 4 +--- arch/x86/kvm/svm/svm.c | 19 ++++++++++++++++++- 4 files changed, 30 insertions(+), 12 deletions(-) diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h index 6ce160ffa678..6301f79fcbae 100644 --- a/arch/x86/kvm/hyperv.h +++ b/arch/x86/kvm/hyperv.h @@ -305,14 +305,6 @@ static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu) { return false; } -static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu) -{ - return false; -} -static inline bool guest_hv_cpuid_has_l2_tlb_flush(struct kvm_vcpu *vcpu) -{ - return false; -} static inline int kvm_hv_verify_vp_assist(struct kvm_vcpu *vcpu) { return 0; diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h index d3f8bfc05832..9af03970d40c 100644 --- a/arch/x86/kvm/svm/hyperv.h +++ b/arch/x86/kvm/svm/hyperv.h @@ -41,6 +41,13 @@ static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu) return hv_vcpu->vp_assist_page.nested_control.features.directhypercall; } +static inline bool nested_svm_is_l2_tlb_flush_hcall(struct kvm_vcpu *vcpu) +{ + return guest_hv_cpuid_has_l2_tlb_flush(vcpu) && + nested_svm_l2_tlb_flush_enabled(vcpu) && + kvm_hv_is_tlb_flush_hcall(vcpu); +} + void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu); #else /* CONFIG_KVM_HYPERV */ static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu) {} @@ -48,6 +55,10 @@ static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu) { return false; } +static inline bool nested_svm_is_l2_tlb_flush_hcall(struct kvm_vcpu *vcpu) +{ + return false; +} static inline void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu) {} #endif /* CONFIG_KVM_HYPERV */ diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 53ab6ce3cc26..750bf93c5341 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -1674,9 +1674,7 @@ int nested_svm_exit_special(struct vcpu_svm *svm) } case SVM_EXIT_VMMCALL: /* Hyper-V L2 TLB flush hypercall is handled by L0 */ - if (guest_hv_cpuid_has_l2_tlb_flush(vcpu) && - nested_svm_l2_tlb_flush_enabled(vcpu) && - kvm_hv_is_tlb_flush_hcall(vcpu)) + if (nested_svm_is_l2_tlb_flush_hcall(vcpu)) return NESTED_EXIT_HOST; break; default: diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 8f8bc863e214..38a2fad81ad8 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -52,6 +52,7 @@ #include "svm.h" #include "svm_ops.h" +#include "hyperv.h" #include "kvm_onhyperv.h" #include "svm_onhyperv.h" @@ -3228,6 +3229,22 @@ static int bus_lock_exit(struct kvm_vcpu *vcpu) return 0; } +static int vmmcall_interception(struct kvm_vcpu *vcpu) +{ + /* + * Inject a #UD if L2 is active and the VMMCALL isn't a Hyper-V TLB + * hypercall, as VMMCALL #UDs if it's not intercepted, and this path is + * reachable if and only if L1 doesn't want to intercept VMMCALL or has + * enabled L0 (KVM) handling of Hyper-V L2 TLB flush hypercalls. + */ + if (is_guest_mode(vcpu) && !nested_svm_is_l2_tlb_flush_hcall(vcpu)) { + kvm_queue_exception(vcpu, UD_VECTOR); + return 1; + } + + return kvm_emulate_hypercall(vcpu); +} + static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { [SVM_EXIT_READ_CR0] = cr_interception, [SVM_EXIT_READ_CR3] = cr_interception, @@ -3278,7 +3295,7 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { [SVM_EXIT_TASK_SWITCH] = task_switch_interception, [SVM_EXIT_SHUTDOWN] = shutdown_interception, [SVM_EXIT_VMRUN] = vmrun_interception, - [SVM_EXIT_VMMCALL] = kvm_emulate_hypercall, + [SVM_EXIT_VMMCALL] = vmmcall_interception, [SVM_EXIT_VMLOAD] = vmload_interception, [SVM_EXIT_VMSAVE] = vmsave_interception, [SVM_EXIT_STGI] = stgi_interception, -- 2.53.0.473.g4a7958ca14-goog