linux-kernel - Re: [PATCH v1] virtio-pci: Fix legacy device flag setting error in probe

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Message-ID: <20230720131423-mutt-send-email-mst@kernel.org>
Date:   Thu, 20 Jul 2023 13:14:41 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Feng Liu <feliu@...dia.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Bodong Wang <bodong@...dia.com>,
        Parav Pandit <parav@...dia.com>, Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH v1] virtio-pci: Fix legacy device flag setting error in
 probe

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@...dia.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@...dia.com>
> > Reviewed-by: Parav Pandit <parav@...dia.com>
> > Reviewed-by: Jiri Pirko <jiri@...dia.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?

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