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

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Date:   Wed, 09 Dec 2020 12:12:31 -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)

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)

>> 
>> 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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