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Message-ID: <aLgIH8i9r7jnYnj1@yzhao56-desk.sh.intel.com>
Date: Wed, 3 Sep 2025 17:19:27 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "seanjc@...gle.com"
<seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>,
"ackerleytng@...gle.com" <ackerleytng@...gle.com>, "Annapurve, Vishal"
<vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "Weiny, Ira" <ira.weiny@...el.com>,
"pbonzini@...hat.com" <pbonzini@...hat.com>, "michael.roth@....com"
<michael.roth@....com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH v2 12/18] KVM: TDX: Bug the VM if extended the
initial measurement fails
> From 0d1ba6d60315e34bdb0e54acceb6e8dd0fbdb262 Mon Sep 17 00:00:00 2001
> From: Yan Zhao <yan.y.zhao@...el.com>
> Date: Tue, 2 Sep 2025 18:31:27 -0700
> Subject: [PATCH 1/2] KVM: TDX: Fix list_add corruption during vcpu_load()
>
> During vCPU creation, a vCPU may be destroyed immediately after
> kvm_arch_vcpu_create() (e.g., due to vCPU id confiliction). However, the
> vcpu_load() inside kvm_arch_vcpu_create() may have associate the vCPU to
> pCPU via "list_add(&tdx->cpu_list, &per_cpu(associated_tdvcpus, cpu))"
> before invoking tdx_vcpu_free().
>
> Though there's no need to invoke tdh_vp_flush() on the vCPU, failing to
> dissociate the vCPU from pCPU (i.e., "list_del(&to_tdx(vcpu)->cpu_list)")
> will cause list corruption of the per-pCPU list associated_tdvcpus.
>
> Then, a later list_add() during vcpu_load() would detect list corruption
> and print calltrace as shown below.
>
> Dissociate a vCPU from its associated pCPU in tdx_vcpu_free() for the vCPUs
> destroyed immediately after creation which must be in
> VCPU_TD_STATE_UNINITIALIZED state.
>
> kernel BUG at lib/list_debug.c:29!
> Oops: invalid opcode: 0000 [#2] SMP NOPTI
> RIP: 0010:__list_add_valid_or_report+0x82/0xd0
>
> Call Trace:
> <TASK>
> tdx_vcpu_load+0xa8/0x120
> vt_vcpu_load+0x25/0x30
> kvm_arch_vcpu_load+0x81/0x300
> vcpu_load+0x55/0x90
> kvm_arch_vcpu_create+0x24f/0x330
> kvm_vm_ioctl_create_vcpu+0x1b1/0x53
> ? trace_lock_release+0x6d/0xb0
> kvm_vm_ioctl+0xc2/0xa60
> ? tty_ldisc_deref+0x16/0x20
> ? debug_smp_processor_id+0x17/0x20
> ? __fget_files+0xc2/0x1b0
> ? debug_smp_processor_id+0x17/0x20
> ? rcu_is_watching+0x13/0x70
> ? __fget_files+0xc2/0x1b0
> ? trace_lock_release+0x6d/0xb0
> ? lock_release+0x14/0xd0
> ? __fget_files+0xcc/0x1b0
> __x64_sys_ioctl+0x9a/0xf0
> ? rcu_is_watching+0x13/0x70
> x64_sys_call+0x10ee/0x20d0
> do_syscall_64+0xc3/0x470
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
Fixes: d789fa6efac9 ("KVM: TDX: Handle vCPU dissociation")
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> ---
> arch/x86/kvm/vmx/tdx.c | 42 +++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 37 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index e99d07611393..99381c8b4108 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -837,19 +837,51 @@ void tdx_vcpu_put(struct kvm_vcpu *vcpu)
> tdx_prepare_switch_to_host(vcpu);
> }
>
> +/*
> + * Life cycles for a TD and a vCPU:
> + * 1. KVM_CREATE_VM ioctl.
> + * TD state is TD_STATE_UNINITIALIZED.
> + * hkid is not assigned at this stage.
> + * 2. KVM_TDX_INIT_VM ioctl.
> + * TD transistions to TD_STATE_INITIALIZED.
> + * hkid is assigned after this stage.
> + * 3. KVM_CREATE_VCPU ioctl. (only when TD is TD_STATE_INITIALIZED).
> + * 3.1 tdx_vcpu_create() transitions vCPU state to VCPU_TD_STATE_UNINITIALIZED.
> + * 3.2 vcpu_load() and vcpu_put() in kvm_arch_vcpu_create().
> + * 3.3 (conditional) if any error encountered after kvm_arch_vcpu_create()
> + * kvm_arch_vcpu_destroy() --> tdx_vcpu_free().
> + * 4. KVM_TDX_INIT_VCPU ioctl.
> + * tdx_vcpu_init() transistions vCPU state to VCPU_TD_STATE_INITIALIZED.
> + * vCPU control structures are allocated at this stage.
> + * 5. kvm_destroy_vm().
> + * 5.1 tdx_mmu_release_hkid(): (1) tdh_vp_flush(), disassociats all vCPUs.
> + * (2) puts hkid to !assigned state.
> + * 5.2 kvm_destroy_vcpus() --> tdx_vcpu_free():
> + * transistions vCPU to VCPU_TD_STATE_UNINITIALIZED state.
> + * 5.3 tdx_vm_destroy()
> + * transitions TD to TD_STATE_UNINITIALIZED state.
> + *
> + * tdx_vcpu_free() can be invoked only at 3.3 or 5.2.
> + * - If at 3.3, hkid is still assigned, but the vCPU must be in
> + * VCPU_TD_STATE_UNINITIALIZED state.
> + * - if at 5.2, hkid must be !assigned and all vCPUs must be in
> + * VCPU_TD_STATE_INITIALIZED state and have been dissociated.
> + */
> void tdx_vcpu_free(struct kvm_vcpu *vcpu)
> {
> struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> struct vcpu_tdx *tdx = to_tdx(vcpu);
> int i;
>
> + if (vcpu->cpu != -1) {
> + KVM_BUG_ON(tdx->state == VCPU_TD_STATE_INITIALIZED, vcpu->kvm);
> + tdx_disassociate_vp(vcpu);
Sorry, I should use "tdx_flush_vp_on_cpu(vcpu);" here to ensure the list_del()
is running on vcpu->cpu with local irq disabled.
> + return;
> + }
> /*
> * It is not possible to reclaim pages while hkid is assigned. It might
> - * be assigned if:
> - * 1. the TD VM is being destroyed but freeing hkid failed, in which
> - * case the pages are leaked
> - * 2. TD VCPU creation failed and this on the error path, in which case
> - * there is nothing to do anyway
> + * be assigned if the TD VM is being destroyed but freeing hkid failed,
> + * in which case the pages are leaked.
> */
> if (is_hkid_assigned(kvm_tdx))
> return;
> --
> 2.43.0
>
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