From: Sean Christopherson Date: Tue, 10 Mar 2026 23:48:12 +0000 (-0700) Subject: KVM: SEV: Disallow LAUNCH_FINISH if vCPUs are actively being created X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=624bf3440d7214b62c22d698a0a294323f331d5d;p=thirdparty%2Fkernel%2Fstable.git KVM: SEV: Disallow LAUNCH_FINISH if vCPUs are actively being created Reject LAUNCH_FINISH for SEV-ES and SNP VMs if KVM is actively creating one or more vCPUs, as KVM needs to process and encrypt each vCPU's VMSA. Letting userspace create vCPUs while LAUNCH_FINISH is in-progress is "fine", at least in the current code base, as kvm_for_each_vcpu() operates on online_vcpus, LAUNCH_FINISH (all SEV+ sub-ioctls) holds kvm->mutex, and fully onlining a vCPU in kvm_vm_ioctl_create_vcpu() is done under kvm->mutex. I.e. there's no difference between an in-progress vCPU and a vCPU that is created entirely after LAUNCH_FINISH. However, given that concurrent LAUNCH_FINISH and vCPU creation can't possibly work (for any reasonable definition of "work"), since userspace can't guarantee whether a particular vCPU will be encrypted or not, disallow the combination as a hardening measure, to reduce the probability of introducing bugs in the future, and to avoid having to reason about the safety of future changes related to LAUNCH_FINISH. Cc: Jethro Beekman Closes: https://lore.kernel.org/all/b31f7c6e-2807-4662-bcdd-eea2c1e132fa@fortanix.com Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260310234829.2608037-5-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 9265ebd9aa186..10b12db7f902d 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1032,6 +1032,9 @@ static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp) if (!sev_es_guest(kvm)) return -ENOTTY; + if (kvm_is_vcpu_creation_in_progress(kvm)) + return -EBUSY; + kvm_for_each_vcpu(i, vcpu, kvm) { ret = mutex_lock_killable(&vcpu->mutex); if (ret) @@ -2052,8 +2055,8 @@ static int sev_check_source_vcpus(struct kvm *dst, struct kvm *src) struct kvm_vcpu *src_vcpu; unsigned long i; - if (src->created_vcpus != atomic_read(&src->online_vcpus) || - dst->created_vcpus != atomic_read(&dst->online_vcpus)) + if (kvm_is_vcpu_creation_in_progress(src) || + kvm_is_vcpu_creation_in_progress(dst)) return -EBUSY; if (!sev_es_guest(src)) @@ -2452,6 +2455,9 @@ static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp) unsigned long i; int ret; + if (kvm_is_vcpu_creation_in_progress(kvm)) + return -EBUSY; + data.gctx_paddr = __psp_pa(sev->snp_context); data.page_type = SNP_PAGE_TYPE_VMSA; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 34759a262b289..3c7f8557f7af5 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1029,6 +1029,13 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id) return NULL; } +static inline bool kvm_is_vcpu_creation_in_progress(struct kvm *kvm) +{ + lockdep_assert_held(&kvm->lock); + + return kvm->created_vcpus != atomic_read(&kvm->online_vcpus); +} + void kvm_destroy_vcpus(struct kvm *kvm); int kvm_trylock_all_vcpus(struct kvm *kvm);