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Message-ID: <20251017003244.186495-25-seanjc@google.com>
Date: Thu, 16 Oct 2025 17:32:42 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>,
Huacai Chen <chenhuacai@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>,
Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>, Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>, "Kirill A. Shutemov" <kas@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
kvm@...r.kernel.org, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
linux-riscv@...ts.infradead.org, x86@...nel.org, linux-coco@...ts.linux.dev,
linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
Kai Huang <kai.huang@...el.com>, Michael Roth <michael.roth@....com>,
Yan Zhao <yan.y.zhao@...el.com>, Vishal Annapurve <vannapurve@...gle.com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>, Ackerley Tng <ackerleytng@...gle.com>,
Binbin Wu <binbin.wu@...ux.intel.com>
Subject: [PATCH v3 24/25] KVM: TDX: Guard VM state transitions with "all" the locks
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 <yan.y.zhao@...el.com>
Closes: https://lore.kernel.org/all/aLFiPq1smdzN3Ary@yzhao56-desk.sh.intel.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/kvm/vmx/tdx.c | 63 +++++++++++++++++++++++++++++++++++-------
1 file changed, 53 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 84b5fe654c99..d6541b08423f 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2632,6 +2632,46 @@ 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);
@@ -2644,6 +2684,10 @@ static int tdx_td_init(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
BUILD_BUG_ON(sizeof(*init_vm) != 256 + sizeof_field(struct kvm_tdx_init_vm, cpuid));
BUILD_BUG_ON(sizeof(struct td_params) != 1024);
+ CLASS(tdx_vm_state_guard, guard)(kvm);
+ if (IS_ERR(guard))
+ return PTR_ERR(guard);
+
if (kvm_tdx->state != TD_STATE_UNINITIALIZED)
return -EINVAL;
@@ -2743,7 +2787,9 @@ 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);
+ 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;
@@ -2781,8 +2827,6 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
if (r)
return r;
- guard(mutex)(&kvm->lock);
-
switch (tdx_cmd.id) {
case KVM_TDX_CAPABILITIES:
r = tdx_get_capabilities(&tdx_cmd);
@@ -3090,8 +3134,6 @@ 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;
@@ -3147,7 +3189,8 @@ 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;
@@ -3155,12 +3198,13 @@ 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) {
@@ -3177,7 +3221,6 @@ int tdx_vcpu_unlocked_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
vcpu_put(vcpu);
- mutex_unlock(&vcpu->mutex);
return r;
}
--
2.51.0.858.gf9c4a03a3a-goog
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