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

Open Source and information security mailing list archives

Date:   Wed, 9 Dec 2020 12:15:25 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Will Deacon <will@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org
Subject: Re: [GIT PULL] IOMMU fix for 5.10 (-final)

On Wed, Dec 9, 2020 at 12:12 PM Jerry Snitselaar <jsnitsel@...hat.com> wrote:
>
>
> Will Deacon @ 2020-12-09 11:50 MST:
>
> > 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)
>
> Since the field in the device table entry format expects it to be n
> where there are 2^n entries in the table I guess it should be:
>
> #define DTE_IRQ_TABLE_LEN 9
> #define MAX_IRQS_PER_TABLE (1 << DTE_IRQ_TABLE_LEN)
>
No, ignore that. I'm being stupid.


> >>
> >> 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
> > _______________________________________________
> > iommu mailing list
> > iommu@...ts.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/iommu
>

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