linux-kernel - Re: Why do we mark vpending table as non-shareable in GICR

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Message-ID: <867eb09i00.wl-marc.zyngier@arm.com>
Date:   Thu, 09 May 2019 08:58:23 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Heyi Guo <guoheyi@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>,
        Christoffer Dall <christoffer.dall@....com>,
        wanghaibin 00208455 <wanghaibin.wang@...wei.com>
Subject: Re: Why do we mark vpending table as non-shareable in GICR_VPENDBASER?

On Thu, 09 May 2019 08:10:09 +0100,
Heyi Guo <guoheyi@...wei.com> wrote:
> 
> Hi Marc,
> 
> We can see in its_vpe_schedule() the shareability bits of
> GICR_VPENDBASER are set as non-shareable, But we set physical
> PENDBASER as inner-shareable. Is there any special reason for doing
> this? If it is because the vpending table is GICR specific, why
> don't we do the same for physical pending table?

That's a good question. They should have similar attributes.

> We have not seen function issue with this setting, but a special
> detector in our hardware warns us that there are non-shareable
> requests sent out while some inner shareable cache entries still
> present in the cache, and it may cause data inconsistent.

The main issue with the inner-shareable attributes and the GIC is that
nothing in the spec says that CPUs and GIC have to be in the same
inner-shareable domain, as the system can have as many as you want.

You obviously have built it with GICR in the same inner-shareability
domain as the CPU. I'm happy to change the VPENDBASER attributes,
given that the CPU has a mapping to that memory already, and that
shouldn't affect systems where GICR isn't in the same inner shareable
domain anyway.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.