linux-kernel - RE: [patch V2 25/33] PCI/MSI: Provide post-enable dynamic allocation interfaces for MSI-X

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Message-ID: <87r0xsd8j4.ffs@tglx>
Date:   Thu, 24 Nov 2022 10:08:31 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>
Subject: RE: [patch V2 25/33] PCI/MSI: Provide post-enable dynamic
 allocation interfaces for MSI-X

On Thu, Nov 24 2022 at 02:58, Kevin Tian wrote:
>> +
>> +/**
>> + * pci_msix_free_irq - Free an interrupt on a PCI/MSIX interrupt domain
>> + *		      which was allocated via pci_msix_alloc_irq_at()
>> + *
>> + * @dev:	The PCI device to operate on
>> + * @map:	A struct msi_map describing the interrupt to free
>> + *		as returned from the allocation function.
>> + */
>
> Can this be used on preallocated descriptors? If not any guard required
> or just treat it as a driver responsibility to not misuse?

The preallocated descriptors are only relevant during setup, but not
post setup. So yes, you can do:

pci_alloc_irq_vectors(dev, 10, 10, PCI_IRQ_MSIX);

and then

    map = { .index = 9, .virq = $IRQ };
    pci_msix_free_irq(dev, &map);

It just works.

>> +void pci_msix_free_irq(struct pci_dev *dev, struct msi_map map)
>> +{
>> +	if (WARN_ON_ONCE(map.index < 0 || map.virq <= 0))
>
> map.virq cannot be negative.

Why? Callers can make up whatever they want, no?

Thanks,

        tglx