Re: [patch V2 02/23] PCI/MSI: Fix pci_irq_vector()/pci_irq_get_affinity()

[Bjorn Helgaas <helgaas@xxxxxxxxxx>]

On Mon, Dec 06, 2021 at 11:27:26PM +0100, Thomas Gleixner wrote:
> pci_irq_vector() and pci_irq_get_affinity() use the list position to find the
> MSI-X descriptor at a given index. That's correct for the normal case where
> the entry number is the same as the list position.
> 
> But it's wrong for cases where MSI-X was allocated with an entries array
> describing sparse entry numbers into the hardware message descriptor
> table. That's inconsistent at best.
> 
> Make it always check the entry number because that's what the zero base
> index really means. This change won't break existing users which use a
> sparse entries array for allocation because these users retrieve the Linux
> interrupt number from the entries array after allocation and none of them
> uses pci_irq_vector() or pci_irq_get_affinity().
> 
> Fixes: aff171641d18 ("PCI: Provide sensible IRQ vector alloc/free routines")
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Tested-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

> ---
> V2: Fix typo in subject - Jason
> ---
>  drivers/pci/msi.c |   26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
> 
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -1187,19 +1187,24 @@ EXPORT_SYMBOL(pci_free_irq_vectors);
>  
>  /**
>   * pci_irq_vector - return Linux IRQ number of a device vector
> - * @dev: PCI device to operate on
> - * @nr: device-relative interrupt vector index (0-based).
> + * @dev:     PCI device to operate on
> + * @nr:              Interrupt vector index (0-based)
> + *
> + * @nr has the following meanings depending on the interrupt mode:
> + *   MSI-X:  The index in the MSI-X vector table
> + *   MSI:    The index of the enabled MSI vectors
> + *   INTx:   Must be 0
> + *
> + * Return: The Linux interrupt number or -EINVAl if @nr is out of range.
>   */
>  int pci_irq_vector(struct pci_dev *dev, unsigned int nr)
>  {
>       if (dev->msix_enabled) {
>               struct msi_desc *entry;
> -             int i = 0;
>  
>               for_each_pci_msi_entry(entry, dev) {
> -                     if (i == nr)
> +                     if (entry->msi_attrib.entry_nr == nr)
>                               return entry->irq;
> -                     i++;
>               }
>               WARN_ON_ONCE(1);
>               return -EINVAL;
> @@ -1223,17 +1228,22 @@ EXPORT_SYMBOL(pci_irq_vector);
>   * pci_irq_get_affinity - return the affinity of a particular MSI vector
>   * @dev:     PCI device to operate on
>   * @nr:              device-relative interrupt vector index (0-based).
> + *
> + * @nr has the following meanings depending on the interrupt mode:
> + *   MSI-X:  The index in the MSI-X vector table
> + *   MSI:    The index of the enabled MSI vectors
> + *   INTx:   Must be 0
> + *
> + * Return: A cpumask pointer or NULL if @nr is out of range
>   */
>  const struct cpumask *pci_irq_get_affinity(struct pci_dev *dev, int nr)
>  {
>       if (dev->msix_enabled) {
>               struct msi_desc *entry;
> -             int i = 0;
>  
>               for_each_pci_msi_entry(entry, dev) {
> -                     if (i == nr)
> +                     if (entry->msi_attrib.entry_nr == nr)
>                               return &entry->affinity->mask;
> -                     i++;
>               }
>               WARN_ON_ONCE(1);
>               return NULL;
>