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KVM: x86/xen: Fix SRCU/RCU usage in readers of evtchn_ports

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The evtchnfd structure itself must be protected by either kvm->lock or
SRCU. Use the former in kvm_xen_eventfd_update(), since the lock is
being taken anyway; kvm_xen_hcall_evtchn_send() instead is a reader and
does not need kvm->lock, and is called in SRCU critical section from the
kvm_x86_handle_exit function.

It is also important to use rcu_read_{lock,unlock}() in
kvm_xen_hcall_evtchn_send(), because idr_remove() will *not*
use synchronize_srcu() to wait for readers to complete.

Remove a superfluous if (kvm) check before calling synchronize_srcu()
in kvm_xen_eventfd_deassign() where kvm has been dereferenced already.

Co-developed-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20221226120320.1125390-3-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2022-12-26 12:03:17 +00:00
parent 92c58965e9
commit 70eae03087
1 changed files with 18 additions and 11 deletions
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29
arch/x86/kvm/xen.c
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@ -1808,20 +1808,23 @@ static int kvm_xen_eventfd_update(struct kvm *kvm,
{
u32 port = data->u.evtchn.send_port;
struct evtchnfd *evtchnfd;
int ret;
if (!port || port >= max_evtchn_port(kvm))
return -EINVAL;
/* Protect writes to evtchnfd as well as the idr lookup. */
mutex_lock(&kvm->lock);
evtchnfd = idr_find(&kvm->arch.xen.evtchn_ports, port);
mutex_unlock(&kvm->lock);
ret = -ENOENT;
if (!evtchnfd)
return -ENOENT;
goto out_unlock;
/* For an UPDATE, nothing may change except the priority/vcpu */
ret = -EINVAL;
if (evtchnfd->type != data->u.evtchn.type)
return -EINVAL;
goto out_unlock;
/*
* Port cannot change, and if it's zero that was an eventfd
@ -1829,20 +1832,21 @@ static int kvm_xen_eventfd_update(struct kvm *kvm,
*/
if (!evtchnfd->deliver.port.port ||
evtchnfd->deliver.port.port != data->u.evtchn.deliver.port.port)
return -EINVAL;
goto out_unlock;
/* We only support 2 level event channels for now */
if (data->u.evtchn.deliver.port.priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL)
return -EINVAL;
goto out_unlock;
mutex_lock(&kvm->lock);
evtchnfd->deliver.port.priority = data->u.evtchn.deliver.port.priority;
if (evtchnfd->deliver.port.vcpu_id != data->u.evtchn.deliver.port.vcpu) {
evtchnfd->deliver.port.vcpu_id = data->u.evtchn.deliver.port.vcpu;
evtchnfd->deliver.port.vcpu_idx = -1;
}
ret = 0;
out_unlock:
mutex_unlock(&kvm->lock);
return 0;
return ret;
}
/*
@ -1935,8 +1939,7 @@ static int kvm_xen_eventfd_deassign(struct kvm *kvm, u32 port)
if (!evtchnfd)
return -ENOENT;
if (kvm)
synchronize_srcu(&kvm->srcu);
synchronize_srcu(&kvm->srcu);
if (!evtchnfd->deliver.port.port)
eventfd_ctx_put(evtchnfd->deliver.eventfd.ctx);
kfree(evtchnfd);
@ -1989,14 +1992,18 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r)
/* Sanity check: this structure is the same for 32-bit and 64-bit */
BUILD_BUG_ON(sizeof(send) != 4);
if (kvm_read_guest_virt(vcpu, param, &send, sizeof(send), &e)) {
*r = -EFAULT;
return true;
}
/* The evtchn_ports idr is protected by vcpu->kvm->srcu */
/*
* evtchnfd is protected by kvm->srcu; the idr lookup instead
* is protected by RCU.
*/
rcu_read_lock();
evtchnfd = idr_find(&vcpu->kvm->arch.xen.evtchn_ports, send.port);
rcu_read_unlock();
if (!evtchnfd)
return false;