Re: [PATCH for-4.{19,20}] xen/vpci: fix backport of 53859596c0d3

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.10.2025 10:59, Roger Pau Monne wrote:
> Commit 53859596c0d3 depends on the behavioral change introduced in
> ee2eb6849d50 that inverted the initialization of the MSI-X and header vPCI
> handlers.  53859596c0d3 requires the header to be initialized before MSI-X.
> 
> Change the order of initialization and adjust init_msix() to carve holes
> for the MSI-X tables if necessary, since it will now run after the BARs
> have been possibly mapped into the domain p2m.
> 
> Fixes: f9aea52a9747 ("vpci/msix: improve handling of bogus MSI-X 
> capabilities")
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -1016,7 +1016,7 @@ static int cf_check init_header(struct pci_dev *pdev)
>      pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
>      return rc;
>  }
> -REGISTER_VPCI_INIT(init_header, VPCI_PRIORITY_MIDDLE);
> +REGISTER_VPCI_INIT(init_header, VPCI_PRIORITY_HIGH);
>  
>  /*
>   * Local variables:
> --- a/xen/drivers/vpci/msix.c
> +++ b/xen/drivers/vpci/msix.c
> @@ -792,9 +792,14 @@ static int cf_check init_msix(struct pci_dev *pdev)
>      pdev->vpci->msix = msix;
>      list_add(&msix->next, &d->arch.hvm.msix_tables);
>  
> -    return 0;
> +    /*
> +     * vPCI header initialization will have mapped the whole BAR into the
> +     * p2m, as MSI-X capability was not yet initialized.  Crave a hole for
> +     * the MSI-X table here, so that Xen can trap accesses.
> +     */
> +    return vpci_make_msix_hole(pdev);
>  }
> -REGISTER_VPCI_INIT(init_msix, VPCI_PRIORITY_HIGH);
> +REGISTER_VPCI_INIT(init_msix, VPCI_PRIORITY_MIDDLE);

Aiui this could as well be VPCI_PRIORITY_LOW now, much like in staging init
order between MSI, MSI-X, and ReBar isn't enforced anymore?

Jan