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SubjectRe: [PATCH] KVM: Destroy target device if coalesced MMIO unregistration fails
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On 12/20/2022 11:04 AM, Wang, Wei W wrote:
> On Tuesday, December 20, 2022 1:19 AM, Sean Christopherson wrote:
>> diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c index
>> 0be80c213f7f..5ef88f5a0864 100644
>> --- a/virt/kvm/coalesced_mmio.c
>> +++ b/virt/kvm/coalesced_mmio.c
>> @@ -187,15 +187,17 @@ int
>> kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm,
>> r = kvm_io_bus_unregister_dev(kvm,
>> zone->pio ? KVM_PIO_BUS : KVM_MMIO_BUS, &dev->dev);
>>
>> + kvm_iodevice_destructor(&dev->dev);
>> +
>> /*
>> * On failure, unregister destroys all devices on the
>> * bus _except_ the target device, i.e. coalesced_zones
>> - * has been modified. No need to restart the walk as
>> - * there aren't any zones left.
>> + * has been modified. Bail after destroying the target
>> + * device, there's no need to restart the walk as there
>> + * aren't any zones left.
>> */
>> if (r)
>> break;
>> - kvm_iodevice_destructor(&dev->dev);
>> }
>> }
> Another option is to let kvm_io_bus_unregister_dev handle this, and no need for callers
> to make the extra kvm_iodevice_destructor() call. This simplifies the usage for callers
> (e.g. reducing LOCs and no leakages like this):

One vote for this option : )


>
> diff --git a/include/kvm/iodev.h b/include/kvm/iodev.h
> index d75fc4365746..56619e33251e 100644
> --- a/include/kvm/iodev.h
> +++ b/include/kvm/iodev.h
> @@ -55,10 +55,4 @@ static inline int kvm_iodevice_write(struct kvm_vcpu *vcpu,
> : -EOPNOTSUPP;
> }
>
> -static inline void kvm_iodevice_destructor(struct kvm_io_device *dev)
> -{
> - if (dev->ops->destructor)
> - dev->ops->destructor(dev);
> -}
> -
> #endif /* __KVM_IODEV_H__ */
> diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
> index 0be80c213f7f..d7135a5e76f8 100644
> --- a/virt/kvm/coalesced_mmio.c
> +++ b/virt/kvm/coalesced_mmio.c
> @@ -195,7 +195,6 @@ int kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm,
> */
> if (r)
> break;
> - kvm_iodevice_destructor(&dev->dev);
> }
> }
>
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 2a3ed401ce46..1b277afb545b 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -898,7 +898,6 @@ kvm_deassign_ioeventfd_idx(struct kvm *kvm, enum kvm_bus bus_idx,
> bus = kvm_get_bus(kvm, bus_idx);
> if (bus)
> bus->ioeventfd_count--;
> - ioeventfd_release(p);
> ret = 0;
> break;
> }
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 13e88297f999..582757ebdce6 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -5200,6 +5200,12 @@ static struct notifier_block kvm_reboot_notifier = {
> .priority = 0,
> };
>
> +static void kvm_iodevice_destructor(struct kvm_io_device *dev)
> +{
> + if (dev->ops->destructor)
> + dev->ops->destructor(dev);
> +}
> +
> static void kvm_io_bus_destroy(struct kvm_io_bus *bus)
> {
> int i;
> @@ -5423,7 +5429,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> struct kvm_io_device *dev)
> {
> - int i, j;
> + int i;
> struct kvm_io_bus *new_bus, *bus;
>
> lockdep_assert_held(&kvm->slots_lock);
> @@ -5453,18 +5459,18 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
> synchronize_srcu_expedited(&kvm->srcu);
>
> - /* Destroy the old bus _after_ installing the (null) bus. */
> + /*
> + * If (null) bus is installed, destroy the old bus, including all the
> + * attached devices. Otherwise, destroy the caller's device only.
> + */
> if (!new_bus) {
> pr_err("kvm: failed to shrink bus, removing it completely\n");
> - for (j = 0; j < bus->dev_count; j++) {
> - if (j == i)
> - continue;
> - kvm_iodevice_destructor(bus->range[j].dev);
> - }
> + kvm_io_bus_destroy(bus);
> + return -ENOMEM;
> }
>
> - kfree(bus);
> - return new_bus ? 0 : -ENOMEM;
> + kvm_iodevice_destructor(dev);
> + return 0;
> }
>
> struct kvm_io_device *kvm_io_bus_get_dev(struct kvm *kvm, enum kvm_bus bus_idx,

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