From: David Woodhouse <dwmw@xxxxxxxxxxxx>
In commit 14243b387137a ("KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN
and event channel delivery") the clever version of me left some helpful
notes for those who would come after him:
/*
* For the irqfd workqueue, using the main kvm->lock mutex is
* fine since this function is invoked from kvm_set_irq() with
* no other lock held, no srcu. In future if it will be called
* directly from a vCPU thread (e.g. on hypercall for an IPI)
* then it may need to switch to using a leaf-node mutex for
* serializing the shared_info mapping.
*/
mutex_lock(&kvm->lock);
In commit 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
the other version of me ran straight past that comment without reading it,
and introduced a potential deadlock by taking vcpu->mutex and kvm->lock
in the wrong order.
Solve this as originally suggested, by adding a leaf-node lock in the Xen
state rather than using kvm->lock for it.
Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/xen.c | 65 +++++++++++++++------------------
2 files changed, 30 insertions(+), 36 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2f5bf581d00a..4ef0143fa682 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1115,6 +1115,7 @@ struct msr_bitmap_range {
/* Xen emulation context */
struct kvm_xen {
+ struct mutex xen_lock;
u32 xen_version;
bool long_mode;
bool runstate_update_flag;
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 809b82bdb9c3..8bebc41f8f9e 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -608,26 +608,26 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
if (!IS_ENABLED(CONFIG_64BIT) && data->u.long_mode) {
r = -EINVAL;
} else {
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
kvm->arch.xen.long_mode = !!data->u.long_mode;
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
r = 0;
}
break;
case KVM_XEN_ATTR_TYPE_SHARED_INFO:
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
r = kvm_xen_shared_info_init(kvm, data->u.shared_info.gfn);
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
break;
case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
if (data->u.vector && data->u.vector < 0x10)
r = -EINVAL;
else {
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
kvm->arch.xen.upcall_vector = data->u.vector;
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
r = 0;
}
break;
@@ -637,9 +637,9 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
break;
case KVM_XEN_ATTR_TYPE_XEN_VERSION:
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
kvm->arch.xen.xen_version = data->u.xen_version;
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
r = 0;
break;
@@ -648,9 +648,9 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
r = -EOPNOTSUPP;
break;
}
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
kvm->arch.xen.runstate_update_flag = !!data->u.runstate_update_flag;
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
r = 0;
break;
@@ -665,7 +665,7 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
{
int r = -ENOENT;
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
switch (data->type) {
case KVM_XEN_ATTR_TYPE_LONG_MODE:
@@ -704,7 +704,7 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
break;
}
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
return r;
}
@@ -712,7 +712,7 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
{
int idx, r = -ENOENT;
- mutex_lock(&vcpu->kvm->lock);
+ mutex_lock(&vcpu->kvm->arch.xen.xen_lock);
idx = srcu_read_lock(&vcpu->kvm->srcu);
switch (data->type) {
@@ -940,7 +940,7 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
}
srcu_read_unlock(&vcpu->kvm->srcu, idx);
- mutex_unlock(&vcpu->kvm->lock);
+ mutex_unlock(&vcpu->kvm->arch.xen.xen_lock);
return r;
}
@@ -948,7 +948,7 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
{
int r = -ENOENT;
- mutex_lock(&vcpu->kvm->lock);
+ mutex_lock(&vcpu->kvm->arch.xen.xen_lock);
switch (data->type) {
case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO:
@@ -1031,7 +1031,7 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
break;
}
- mutex_unlock(&vcpu->kvm->lock);
+ mutex_unlock(&vcpu->kvm->arch.xen.xen_lock);
return r;
}
@@ -1124,7 +1124,7 @@ int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc)
xhc->blob_size_32 || xhc->blob_size_64))
return -EINVAL;
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
if (xhc->msr && !kvm->arch.xen_hvm_config.msr)
static_branch_inc(&kvm_xen_enabled.key);
@@ -1133,7 +1133,7 @@ int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc)
memcpy(&kvm->arch.xen_hvm_config, xhc, sizeof(*xhc));
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
return 0;
}
@@ -1676,15 +1676,7 @@ static int kvm_xen_set_evtchn(struct kvm_xen_evtchn *xe, struct kvm *kvm)
mm_borrowed = true;
}
- /*
- * For the irqfd workqueue, using the main kvm->lock mutex is
- * fine since this function is invoked from kvm_set_irq() with
- * no other lock held, no srcu. In future if it will be called
- * directly from a vCPU thread (e.g. on hypercall for an IPI)
- * then it may need to switch to using a leaf-node mutex for
- * serializing the shared_info mapping.
- */
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
/*
* It is theoretically possible for the page to be unmapped
@@ -1713,7 +1705,7 @@ static int kvm_xen_set_evtchn(struct kvm_xen_evtchn *xe, struct kvm *kvm)
srcu_read_unlock(&kvm->srcu, idx);
} while(!rc);
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
if (mm_borrowed)
kthread_unuse_mm(kvm->mm);
@@ -1829,7 +1821,7 @@ static int kvm_xen_eventfd_update(struct kvm *kvm,
int ret;
/* Protect writes to evtchnfd as well as the idr lookup. */
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
evtchnfd = idr_find(&kvm->arch.xen.evtchn_ports, port);
ret = -ENOENT;
@@ -1860,7 +1852,7 @@ static int kvm_xen_eventfd_update(struct kvm *kvm,
}
ret = 0;
out_unlock:
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
return ret;
}
@@ -1923,10 +1915,10 @@ static int kvm_xen_eventfd_assign(struct kvm *kvm,
evtchnfd->deliver.port.priority = data->u.evtchn.deliver.port.priority;
}
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
ret = idr_alloc(&kvm->arch.xen.evtchn_ports, evtchnfd, port, port + 1,
GFP_KERNEL);
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
if (ret >= 0)
return 0;
@@ -1944,9 +1936,9 @@ static int kvm_xen_eventfd_deassign(struct kvm *kvm, u32 port)
{
struct evtchnfd *evtchnfd;
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
evtchnfd = idr_remove(&kvm->arch.xen.evtchn_ports, port);
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
if (!evtchnfd)
return -ENOENT;
@@ -1963,7 +1955,7 @@ static int kvm_xen_eventfd_reset(struct kvm *kvm)
struct evtchnfd *evtchnfd;
int i;
- mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.xen.xen_lock);
idr_for_each_entry(&kvm->arch.xen.evtchn_ports, evtchnfd, i) {
idr_remove(&kvm->arch.xen.evtchn_ports, evtchnfd->send_port);
synchronize_srcu(&kvm->srcu);
@@ -1971,7 +1963,7 @@ static int kvm_xen_eventfd_reset(struct kvm *kvm)
eventfd_ctx_put(evtchnfd->deliver.eventfd.ctx);
kfree(evtchnfd);
}
- mutex_unlock(&kvm->lock);
+ mutex_unlock(&kvm->arch.xen.xen_lock);
return 0;
}
@@ -2063,6 +2055,7 @@ void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
void kvm_xen_init_vm(struct kvm *kvm)
{
+ mutex_init(&kvm->arch.xen.xen_lock);
idr_init(&kvm->arch.xen.evtchn_ports);
kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm, NULL, KVM_HOST_USES_PFN);
}
--
2.35.3
