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Re: [PATCH] arm/its: Decode BASER cacheability field before comparing
- To: Mykola Kvach <xakep.amatop@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 10 Apr 2026 10:07:06 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Mykola Kvach <mykola_kvach@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Mykyta Poturai <mykyta_poturai@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 10 Apr 2026 09:07:20 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/04/2026 8:08 am, Mykola Kvach wrote:
> Hi Jan,
>
> Thank you for the review.
>
> On Fri, Apr 10, 2026 at 9:40 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 10.04.2026 08:09, Mykola Kvach wrote:
>>> --- a/xen/arch/arm/gic-v3-its.c
>>> +++ b/xen/arch/arm/gic-v3-its.c
>>> @@ -496,7 +496,8 @@ retry:
>>> }
>>> attr = regc & BASER_ATTR_MASK;
>>> }
>>> - if ( (regc & GITS_BASER_INNER_CACHEABILITY_MASK) <= GIC_BASER_CACHE_nC
>>> )
>>> + if ( ((regc & GITS_BASER_INNER_CACHEABILITY_MASK) >>
>>> + GITS_BASER_INNER_CACHEABILITY_SHIFT) <= GIC_BASER_CACHE_nC )
>> Are you aware of MASK_EXTR()? This is one of the cases that we have it for.
>> Really all *_SHIFT constants should be purged, as they can be calculated
>> from their *_MASK counterparts (leveraging MASK_{EXTR,INSR}() to keep the
>> code readable).
> I wasn't aware of this macro, thanks. I will take a look.
As a general rule of thumb, where you've got a _MASK/_SHIFT pair, you
should be using MASK_INSR/EXTR and delete the shift constant.
It is is ~half the code (visually), and removes an entire class of
errors (mismatched constants).
~Andrew
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