On Wed, Aug 05, 2026 at 11:29:34AM +0800, Xiong Weimin wrote:
> vp_request_msix_vectors() bumps desc->pre_vectors in place to reserve
> the virtio config vector. vp_find_vqs() may call it more than once while
> retrying MSI-X with different per-vq policies, so the caller's
> irq_affinity keeps accumulating and later attempts get the wrong
> affinity layout.
>
> Copy the descriptor to a stack local, adjust pre_vectors there, and
> pass that to pci_alloc_irq_vectors_affinity().
>
> Fixes: ba74b6f7fcc0 ("virtio_pci: fix cpu affinity support")
> Cc: [email protected]
> Signed-off-by: Xiong Weimin <[email protected]>
> ---
> drivers/virtio/virtio_pci_common.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_common.c
> b/drivers/virtio/virtio_pci_common.c
> index 164f480b1..9e75fd03e 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -128,6 +128,7 @@ static int vp_request_msix_vectors(struct virtio_device
> *vdev, int nvectors,
> {
> struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> const char *name = dev_name(&vp_dev->vdev.dev);
> + struct irq_affinity tmp_aff, *aff = NULL;
"tmp" in what sense? if we can come up with a sensible name, just
"affinity" will do.
> unsigned int flags = PCI_IRQ_MSIX;
> unsigned int i, v;
> int err = -ENOMEM;
> @@ -146,16 +147,19 @@ static int vp_request_msix_vectors(struct virtio_device
> *vdev, int nvectors,
> GFP_KERNEL))
> goto error;
>
> - if (!per_vq_vectors)
> - desc = NULL;
> -
> - if (desc) {
> + if (per_vq_vectors && desc) {
> + /*
> + * Do not mutate the caller's irq_affinity across MSI-X
> + * fallback retries in vp_find_vqs().
> + */
We do not need a comment arguing with previous version of the code.
> + tmp_aff = *desc;
> + tmp_aff.pre_vectors++; /* virtio config vector */
> + aff = &tmp_aff;
just assign to desc, instead?
> flags |= PCI_IRQ_AFFINITY;
> - desc->pre_vectors++; /* virtio config vector */
> }
>
> err = pci_alloc_irq_vectors_affinity(vp_dev->pci_dev, nvectors,
> - nvectors, flags, desc);
> + nvectors, flags, aff);
> if (err < 0)
> goto error;
> vp_dev->msix_enabled = 1;
> --
> 2.43.0
