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

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Message-ID: <63414d91-2ddf-e1bb-22cf-3eb00e355fba@huawei.com>
Date:   Thu, 9 May 2019 16:56:57 +0800
From:   Heyi Guo <guoheyi@...wei.com>
To:     Marc Zyngier <marc.zyngier@....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?

Thanks.

One more question about the cacheability of VPROPBASER, which is RaWb, while it is RaWaWb for PROPBASER. Any special reason for this?

Heyi


On 2019/5/9 15:58, Marc Zyngier wrote:
> 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.
>