linux-kernel - Re: [PATCH v3 1/2] PCI: Add parameter nr_devfns to pci_add_dma

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Date:   Wed, 27 Nov 2019 10:38:42 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     James Sewart <jamessewart@...sta.com>, linux-pci@...r.kernel.org
Cc:     Christoph Hellwig <hch@...radead.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Dmitry Safonov <dima@...sta.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [PATCH v3 1/2] PCI: Add parameter nr_devfns to pci_add_dma_alias



On 2019-11-27 6:27 a.m., James Sewart wrote:
>   * This helper encodes an 8-bit devfn as a bit number in dma_alias_mask
>   * which is used to program permissible bus-devfn source addresses for DMA
> @@ -5873,8 +5874,12 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
>   * cannot be left as a userspace activity).  DMA aliases should therefore
>   * be configured via quirks, such as the PCI fixup header quirk.
>   */
> -void pci_add_dma_alias(struct pci_dev *dev, u8 devfn)
> +void pci_add_dma_alias(struct pci_dev *dev, u8 devfn_from, int nr_devfns)
>  {
> +	int devfn_to = devfn_from + nr_devfns - 1;
> +
> +	BUG_ON(nr_devfns < 1);

Why not just make nr_devfns unsigned and do nothing if it's zero? It
might also be worth checking that nr_devfns + devfn_from is less than
U8_MAX... But I'd probably avoid the BUG_ON and just truncate it.

Logan