Re: [PATCH] PCI/MSI: Size device MSI domain with the maximum number of vectors

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Tue, Jun 03, 2025 at 03:18:01PM +0100, Marc Zyngier wrote:
> Zenghui reports that since 1396e89e09f0 ("genirq/msi: Move prepare()
> call to per-device allocation"), his Multi-MSI capable device isn't
> working anymore.
> 
> This is a consequence of 15c72f824b32 ("PCI/MSI: Add support for
> per device MSI[X] domains"), which always creates a MSI domain of
> size 1, even in the presence of Multi-MSI.
> 
> While this was somehow working until then, moving the .prepare()
> call ends up sizing the ITS table with a tiny value for this device,
> and making the endpoint driver unhappy.
> 
> Instead, always create the domain (and call the .prepare() helper)
> with the maximum expected size.
> 
> Fixes: 1396e89e09f0 ("genirq/msi: Move prepare() call to per-device allocation")
> Fixes: 15c72f824b32 ("PCI/MSI: Add support for per device MSI[X] domains")
> Link: https://lore.kernel.org/r/0b1d7aec-1eac-a9cd-502a-339e216e08a1@huawei.com
> Reported-by: Zenghui Yu <yuzenghui@huawei.com>
> Tested-by: Zenghui Yu <yuzenghui@huawei.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  drivers/pci/msi/irqdomain.c | 5 +++--
>  drivers/pci/msi/msi.c       | 8 ++++----
>  drivers/pci/msi/msi.h       | 2 +-
>  3 files changed, 8 insertions(+), 7 deletions(-)

Reviewed-by: Lorenzo Pieralisi <lpieralisi@kernel.org>

> diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
> index d7ba8795d60f..c05152733993 100644
> --- a/drivers/pci/msi/irqdomain.c
> +++ b/drivers/pci/msi/irqdomain.c
> @@ -271,6 +271,7 @@ static bool pci_create_device_domain(struct pci_dev *pdev, const struct msi_doma
>  /**
>   * pci_setup_msi_device_domain - Setup a device MSI interrupt domain
>   * @pdev:	The PCI device to create the domain on
> + * @hwsize:	The maximum number of MSI vectors
>   *
>   * Return:
>   *  True when:
> @@ -287,7 +288,7 @@ static bool pci_create_device_domain(struct pci_dev *pdev, const struct msi_doma
>   *	- The device is removed
>   *	- MSI is disabled and a MSI-X domain is created
>   */
> -bool pci_setup_msi_device_domain(struct pci_dev *pdev)
> +bool pci_setup_msi_device_domain(struct pci_dev *pdev, unsigned int hwsize)
>  {
>  	if (WARN_ON_ONCE(pdev->msix_enabled))
>  		return false;
> @@ -297,7 +298,7 @@ bool pci_setup_msi_device_domain(struct pci_dev *pdev)
>  	if (pci_match_device_domain(pdev, DOMAIN_BUS_PCI_DEVICE_MSIX))
>  		msi_remove_device_irq_domain(&pdev->dev, MSI_DEFAULT_DOMAIN);
>  
> -	return pci_create_device_domain(pdev, &pci_msi_template, 1);
> +	return pci_create_device_domain(pdev, &pci_msi_template, hwsize);
>  }
>  
>  /**
> diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
> index d6ce04054702..6ede55a7c5e6 100644
> --- a/drivers/pci/msi/msi.c
> +++ b/drivers/pci/msi/msi.c
> @@ -439,16 +439,16 @@ int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
>  	if (nvec < minvec)
>  		return -ENOSPC;
>  
> -	if (nvec > maxvec)
> -		nvec = maxvec;
> -
>  	rc = pci_setup_msi_context(dev);
>  	if (rc)
>  		return rc;
>  
> -	if (!pci_setup_msi_device_domain(dev))
> +	if (!pci_setup_msi_device_domain(dev, nvec))
>  		return -ENODEV;
>  
> +	if (nvec > maxvec)
> +		nvec = maxvec;
> +
>  	for (;;) {
>  		if (affd) {
>  			nvec = irq_calc_affinity_vectors(minvec, nvec, affd);
> diff --git a/drivers/pci/msi/msi.h b/drivers/pci/msi/msi.h
> index fc70b601e942..0b420b319f50 100644
> --- a/drivers/pci/msi/msi.h
> +++ b/drivers/pci/msi/msi.h
> @@ -107,7 +107,7 @@ enum support_mode {
>  };
>  
>  bool pci_msi_domain_supports(struct pci_dev *dev, unsigned int feature_mask, enum support_mode mode);
> -bool pci_setup_msi_device_domain(struct pci_dev *pdev);
> +bool pci_setup_msi_device_domain(struct pci_dev *pdev, unsigned int hwsize);
>  bool pci_setup_msix_device_domain(struct pci_dev *pdev, unsigned int hwsize);
>  
>  /* Legacy (!IRQDOMAIN) fallbacks */
> -- 
> 2.47.2
>