Acquire kvm->lock, kvm->slots_lock, and all vcpu->mutex locks when servicing ioctls that (a) transition the TD to a new state, i.e. when doing INIT or FINALIZE or (b) are only valid if the TD is in a specific state, i.e. when initializing a vCPU or memory region. Acquiring "all" the locks fixes several KVM_BUG_ON() situations where a SEAMCALL can fail due to racing actions, e.g. if tdh_vp_create() contends with either tdh_mr_extend() or tdh_mr_finalize(). For all intents and purposes, the paths in question are fully serialized, i.e. there's no reason to try and allow anything remotely interesting to happen. Smack 'em with a big hammer instead of trying to be "nice". Acquire kvm->lock to prevent VM-wide things from happening, slots_lock to prevent kvm_mmu_zap_all_fast(), and _all_ vCPU mutexes to prevent vCPUs from interefering. Use the recently-renamed kvm_arch_vcpu_unlocked_ioctl() to service the vCPU-scoped ioctls to avoid a lock inversion problem, e.g. due to taking vcpu->mutex outside kvm->lock. See also commit ecf371f8b02d ("KVM: SVM: Reject SEV{-ES} intra host migration if vCPU creation is in-flight"), which fixed a similar bug with SEV intra-host migration where an in-flight vCPU creation could race with a VM-wide state transition. Define a fancy new CLASS to handle the lock+check => unlock logic with guard()-like syntax: CLASS(tdx_vm_state_guard, guard)(kvm); if (IS_ERR(guard)) return PTR_ERR(guard); to simplify juggling the many locks. Note! Take kvm->slots_lock *after* all vcpu->mutex locks, as per KVM's soon-to-be-documented lock ordering rules[1]. Link: https://lore.kernel.org/all/20251016235538.171962-1-seanjc@google.com [1] Reported-by: Yan Zhao Closes: https://lore.kernel.org/all/aLFiPq1smdzN3Ary@yzhao56-desk.sh.intel.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/tdx.c | 59 +++++++++++++++++++++++++++++++++++------- 1 file changed, 49 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 57dfddd2a6cf..8bcdec049ac6 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -2653,6 +2653,46 @@ static int tdx_read_cpuid(struct kvm_vcpu *vcpu, u32 leaf, u32 sub_leaf, return -EIO; } +typedef void *tdx_vm_state_guard_t; + +static tdx_vm_state_guard_t tdx_acquire_vm_state_locks(struct kvm *kvm) +{ + int r; + + mutex_lock(&kvm->lock); + + if (kvm->created_vcpus != atomic_read(&kvm->online_vcpus)) { + r = -EBUSY; + goto out_err; + } + + r = kvm_lock_all_vcpus(kvm); + if (r) + goto out_err; + + /* + * Note the unintuitive ordering! vcpu->mutex must be taken outside + * kvm->slots_lock! + */ + mutex_lock(&kvm->slots_lock); + return kvm; + +out_err: + mutex_unlock(&kvm->lock); + return ERR_PTR(r); +} + +static void tdx_release_vm_state_locks(struct kvm *kvm) +{ + mutex_unlock(&kvm->slots_lock); + kvm_unlock_all_vcpus(kvm); + mutex_unlock(&kvm->lock); +} + +DEFINE_CLASS(tdx_vm_state_guard, tdx_vm_state_guard_t, + if (!IS_ERR(_T)) tdx_release_vm_state_locks(_T), + tdx_acquire_vm_state_locks(kvm), struct kvm *kvm); + static int tdx_td_init(struct kvm *kvm, struct kvm_tdx_cmd *cmd) { struct kvm_tdx_init_vm __user *user_data = u64_to_user_ptr(cmd->data); @@ -2764,8 +2804,6 @@ static int tdx_td_finalize(struct kvm *kvm, struct kvm_tdx_cmd *cmd) { struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm); - guard(mutex)(&kvm->slots_lock); - if (!is_hkid_assigned(kvm_tdx) || kvm_tdx->state == TD_STATE_RUNNABLE) return -EINVAL; @@ -2809,7 +2847,9 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) if (tdx_cmd.id == KVM_TDX_CAPABILITIES) return tdx_get_capabilities(&tdx_cmd); - guard(mutex)(&kvm->lock); + CLASS(tdx_vm_state_guard, guard)(kvm); + if (IS_ERR(guard)) + return PTR_ERR(guard); switch (tdx_cmd.id) { case KVM_TDX_INIT_VM: @@ -3113,8 +3153,6 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c if (tdx->state != VCPU_TD_STATE_INITIALIZED) return -EINVAL; - guard(mutex)(&kvm->slots_lock); - /* Once TD is finalized, the initial guest memory is fixed. */ if (kvm_tdx->state == TD_STATE_RUNNABLE) return -EINVAL; @@ -3170,7 +3208,8 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c int tdx_vcpu_unlocked_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { - struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm); + struct kvm *kvm = vcpu->kvm; + struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm); struct kvm_tdx_cmd cmd; int r; @@ -3178,12 +3217,13 @@ int tdx_vcpu_unlocked_ioctl(struct kvm_vcpu *vcpu, void __user *argp) if (r) return r; + CLASS(tdx_vm_state_guard, guard)(kvm); + if (IS_ERR(guard)) + return PTR_ERR(guard); + if (!is_hkid_assigned(kvm_tdx) || kvm_tdx->state == TD_STATE_RUNNABLE) return -EINVAL; - if (mutex_lock_killable(&vcpu->mutex)) - return -EINTR; - vcpu_load(vcpu); switch (cmd.id) { @@ -3200,7 +3240,6 @@ int tdx_vcpu_unlocked_ioctl(struct kvm_vcpu *vcpu, void __user *argp) vcpu_put(vcpu); - mutex_unlock(&vcpu->mutex); return r; } -- 2.51.1.930.gacf6e81ea2-goog