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

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On 2023-07-19 p.m.10:27, Jason Wang wrote:
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On Wed, Jul 19, 2023 at 11:46 PM Feng Liu <feliu@xxxxxxxxxx> 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@xxxxxxxxxx>
Reviewed-by: Parav Pandit <parav@xxxxxxxxxx>
Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
  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,


-       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);


Hi, Jason

In the case of force_legacy, if no IO space occurs, function will return directly after vp_legacy_probe, and will not run vp_dev->is_legacy = true; because vp_dev is allocated through kzalloc, the default vp_dev->is_legacy is false, which It is expected for modern device, so it will not break modern device.

What do you think?

int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev)

	rc = vp_legacy_probe(ldev);
	if (rc)
		return rc;  /* if no IO space, function will return from here */

	vp_dev->is_legacy = true;

         return 0;
2.37.1 (Apple Git-137.1)

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