linux-kernel - Re: [GIT PULL] IOMMU fix for 5.10 (-final)

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Message-ID: <20201209185020.GC8778@willie-the-truck>
Date:   Wed, 9 Dec 2020 18:50:20 +0000
From:   Will Deacon <will@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        iommu <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [GIT PULL] IOMMU fix for 5.10 (-final)

On Wed, Dec 09, 2020 at 10:07:46AM -0800, Linus Torvalds wrote:
> On Wed, Dec 9, 2020 at 6:12 AM Will Deacon <will@...nel.org> wrote:
> >
> > Please pull this one-liner AMD IOMMU fix for 5.10. It's actually a fix
> > for a fix, where the size of the interrupt remapping table was increased
> > but a related constant for the size of the interrupt table was forgotten.
> 
> Pulled.

Thanks.

> However, why didn't this then add some sanity checking for the two
> different #defines to be in sync?
> 
> IOW, something like
> 
>    #define AMD_IOMMU_IRQ_TABLE_SHIFT 9
> 
>    #define MAX_IRQS_PER_TABLE (1 << AMD_IOMMU_IRQ_TABLE_SHIFT)
>    #define DTE_IRQ_TABLE_LEN ((u64)AMD_IOMMU_IRQ_TABLE_SHIFT << 1)
> 
> or whatever. Hmm?

This looks like a worthwhile change to me, but I don't have any hardware
so I've been very reluctant to make even "obvious" driver changes here.

Suravee -- please can you post a patch implementing the above?

> That way this won't happen again, but perhaps equally importantly the
> linkage will be more clear, and there won't be those random constants.
> 
> Naming above is probably garbage - I assume there's some actual
> architectural name for that irq table length field in the DTE?

The one in the spec is even better: "IntTabLen".

Will