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Date:   Mon, 24 Jul 2023 09:14:29 -0400
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Subject: Re: [PATCH v1] virtio-pci: Fix legacy device flag setting error in
 probe
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        Bodong Wang <bodong@nvidia.com>,
        Parav Pandit <parav@nvidia.com>, Jiri Pirko <jiri@nvidia.com>
References: <20230719154550.79536-1-feliu@nvidia.com>
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From:   Feng Liu <feliu@nvidia.com>
In-Reply-To: <20230720131423-mutt-send-email-mst@kernel.org>
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On 2023-07-20 p.m.1:14, Michael S. Tsirkin wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Thu, Jul 20, 2023 at 10:27:04AM +0800, Jason Wang wrote:
>> On Wed, Jul 19, 2023 at 11:46 PM Feng Liu <feliu@nvidia.com> wrote:
>>>
>>> The 'is_legacy' flag is used to differentiate between legacy vs modern
>>> device. Currently, it is based on the value of vp_dev->ldev.ioaddr.
>>> However, due to the shared memory of the union between struct
>>> virtio_pci_legacy_device and struct virtio_pci_modern_device, when
>>> virtio_pci_modern_probe modifies the content of struct
>>> virtio_pci_modern_device, it affects the content of struct
>>> virtio_pci_legacy_device, and ldev.ioaddr is no longer zero, causing
>>> the 'is_legacy' flag to be set as true. To resolve issue, when legacy
>>> device is probed, mark 'is_legacy' as true, when modern device is
>>> probed, keep 'is_legacy' as false.
>>>
>>> Fixes: 4f0fc22534e3 ("virtio_pci: Optimize virtio_pci_device structure size")
>>> Signed-off-by: Feng Liu <feliu@nvidia.com>
>>> Reviewed-by: Parav Pandit <parav@nvidia.com>
>>> Reviewed-by: Jiri Pirko <jiri@nvidia.com>
>>> ---
>>>   drivers/virtio/virtio_pci_common.c | 2 --
>>>   drivers/virtio/virtio_pci_legacy.c | 1 +
>>>   2 files changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
>>> index a6c86f916dbd..c2524a7207cf 100644
>>> --- a/drivers/virtio/virtio_pci_common.c
>>> +++ b/drivers/virtio/virtio_pci_common.c
>>> @@ -557,8 +557,6 @@ static int virtio_pci_probe(struct pci_dev *pci_dev,
>>>
>>>          pci_set_master(pci_dev);
>>>
>>> -       vp_dev->is_legacy = vp_dev->ldev.ioaddr ? true : false;
>>> -
>>>          rc = register_virtio_device(&vp_dev->vdev);
>>>          reg_dev = vp_dev;
>>>          if (rc)
>>> diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
>>> index 2257f1b3d8ae..d9cbb02b35a1 100644
>>> --- a/drivers/virtio/virtio_pci_legacy.c
>>> +++ b/drivers/virtio/virtio_pci_legacy.c
>>> @@ -223,6 +223,7 @@ int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev)
>>>          vp_dev->config_vector = vp_config_vector;
>>>          vp_dev->setup_vq = setup_vq;
>>>          vp_dev->del_vq = del_vq;
>>> +       vp_dev->is_legacy = true;
>>
>> This seems break force_legacy for modern device:
>>
>>          if (force_legacy) {
>>                  rc = virtio_pci_legacy_probe(vp_dev);
>>                  /* Also try modern mode if we can't map BAR0 (no IO space). */
>>                  if (rc == -ENODEV || rc == -ENOMEM)
>>                          rc = virtio_pci_modern_probe(vp_dev);
>>
>> Thanks
> 
> don't see the breakage here - can you explain a bit more?
> 
Hi, Jason

I also think there is no breakage herea and gave an explanation in 
another email, please have a see.

So are there any comments about this bug fix patch? Can this patch pass 
the review?

Thanks
Feng

>>>
>>>          return 0;
>>>   }
>>> --
>>> 2.37.1 (Apple Git-137.1)
>>>
>