linux-kernel - Re: revert bab65e48cb064 PCI/MSI Sanitize MSI-X checks

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Message-ID: <20230406150742.GA3703273@bhelgaas>
Date:   Thu, 6 Apr 2023 10:07:42 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-pci@...r.kernel.org, regressions@...ts.linux.dev
Subject: Re: revert bab65e48cb064 PCI/MSI Sanitize MSI-X checks

[+cc linux-pci, regressions]

On Thu, Apr 06, 2023 at 11:05:14AM +0000, David Laight wrote:
> The change in bab65e48cb064 breaks pci_enable_msix_range().
> The intent is to optimise the sanity checks, but it is
> somewhat overenthusiastic.
> 
> The interface allows you to ask for a lot of vectors and
> returns the number that were allocated.
> However, after the change, you can't request a vector
> that is higher than the largest the hardware supports.
> Which makes that rather pointless.
> 
> So code like:
> 	for (i = 0; i < 16; i++)
> 		msix_tbl[i].entry = i;
> 	nvec = pci_enable_msix_range(dev, msix_tbl, 1, 16);
> Now returns -22 if the hardware only supports 8 interrupts.
> 
> Previously it returned 8.
> 
> I can fix my driver, but I suspect that any code that relies
> on a smaller number of vectors being returned is now broken.

Thanks for the report!  bab65e48cb06 ("PCI/MSI: Sanitize MSI-X
checks") appeared in v6.2-rc1, so this is a recent regression and it
would be good to fix it for v6.3.

bab65e48cb06 only touches drivers/pci/msi/msi.c, but since it didn't
go through the PCI tree, I'll let Thomas handle any revert (or better,
an improvement to pci_msix_validate_entries()) since he wrote and
applied the original.

Bjorn