linux-kernel - Re: [PATCH] virtio: Remove virtio devices on device

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Message-ID: <6bce0f4c-636f-456b-ab21-4a25d3dc8803@redhat.com>
Date: Thu, 6 Feb 2025 09:59:58 +0100
From: Eric Auger <eauger@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Zhenzhong Duan <zhenzhong.duan@...el.com>, virtualization@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Hongyu Ning <hongyu.ning@...ux.intel.com>
Subject: Re: [PATCH] virtio: Remove virtio devices on device_shutdown()

Hi,

On 2/4/25 12:46 PM, Eric Auger wrote:
> Hi,
> 
> On 2/3/25 3:48 PM, Michael S. Tsirkin wrote:
>> On Fri, Jan 31, 2025 at 10:53:15AM +0100, Eric Auger wrote:
>>> Hi Kirill, Michael
>>>
>>> On 8/8/24 9:51 AM, Kirill A. Shutemov wrote:
>>>> Hongyu reported a hang on kexec in a VM. QEMU reported invalid memory
>>>> accesses during the hang.
>>>>
>>>> 	Invalid read at addr 0x102877002, size 2, region '(null)', reason: rejected
>>>> 	Invalid write at addr 0x102877A44, size 2, region '(null)', reason: rejected
>>>> 	...
>>>>
>>>> It was traced down to virtio-console. Kexec works fine if virtio-console
>>>> is not in use.
>>>>
>>>> Looks like virtio-console continues to write to the MMIO even after
>>>> underlying virtio-pci device is removed.
>>>>
>>>> The problem can be mitigated by removing all virtio devices on virtio
>>>> bus shutdown.
>>>>
>>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>>>> Reported-by: Hongyu Ning <hongyu.ning@...ux.intel.com>
>>>
>>> Gentle ping on that patch that seems to have fallen though the cracks.
>>>
>>> I think this fix is really needed. I have another test case with a
>>> rebooting guest exposed with virtio-net (backed by vhost-net) and
>>> viommu. Since there is currently no shutdown for the virtio-net, on
>>> reboot, the IOMMU is disabled through the native_machine_shutdown()/
>>> x86_platform.iommu_shutdown() while the virtio-net is still alive.
>>>
>>> Normally device_shutdown() should call virtio-net shutdown before the
>>> IOMMU tear down and we wouldn't see any spurious transactions after
>>> iommu shutdown.
>>>
>>> With that fix, the above test case is fixed and I do not see spurious
>>> vhost IOTLB miss spurious requests.
>>>
>>> For more details, see qemu thread ([PATCH] hw/virtio/vhost: Disable
>>> IOTLB callbacks when IOMMU gets disabled,
>>> https://lore.kernel.org/all/20250120173339.865681-1-eric.auger@redhat.com/)
>>>
>>>
>>> Reviewed-by: Eric Auger <eric.auger@...hat.com>
>>> Tested-by: Eric Auger <eric.auger@...hat.com>
>>>
>>> Thanks
>>>
>>> Eric
>>>
>>>> ---
>>>>  drivers/virtio/virtio.c | 10 ++++++++++
>>>>  1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
>>>> index a9b93e99c23a..6c2f908eb22c 100644
>>>> --- a/drivers/virtio/virtio.c
>>>> +++ b/drivers/virtio/virtio.c
>>>> @@ -356,6 +356,15 @@ static void virtio_dev_remove(struct device *_d)
>>>>  	of_node_put(dev->dev.of_node);
>>>>  }
>>>>  
>>>> +static void virtio_dev_shutdown(struct device *_d)
>>>> +{
>>>> +	struct virtio_device *dev = dev_to_virtio(_d);
>>>> +	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
>>>> +
>>>> +	if (drv && drv->remove)
>>>> +		drv->remove(dev);
>>
>>
>> I am concerned that full remove is a heavyweight operation.
>> Do not want to slow down reboots even more.
>> How about just doing a reset, instead?
> 
> I tested with
> 
> static void virtio_dev_shutdown(struct device *_d)
> {
>         struct virtio_device *dev = dev_to_virtio(_d);
> 
>         virtio_reset_device(dev);
> }
> 
> 
> and it fixes my issue.
> 
> Kirill, would that fix you issue too?
gentle ping.

this also fixes another issue with qemu vSMMU + virtio-scsi-pci. With
the above addition I get rid of spurious warning in qemu on guest reboot.

qemu-system-aarch64: virtio: zero sized buffers are not allowed
qemu-system-aarch64: vhost vring error in virtqueue 0: Invalid argument (22)

Would you mind if I respin?

Thanks

Eric




> 
> Thanks
> 
> Eric
>>
>>>> +}
>>>> +
>>>>  static const struct bus_type virtio_bus = {
>>>>  	.name  = "virtio",
>>>>  	.match = virtio_dev_match,
>>>> @@ -363,6 +372,7 @@ static const struct bus_type virtio_bus = {
>>>>  	.uevent = virtio_uevent,
>>>>  	.probe = virtio_dev_probe,
>>>>  	.remove = virtio_dev_remove,
>>>> +	.shutdown = virtio_dev_shutdown,
>>>>  };
>>>>  
>>>>  int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
>>
>