linux-kernel - Re: [PATCH] irqchip/gic-v4: Fix non-stick page size error for setup GITS

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Date:   Mon, 16 Mar 2020 08:47:14 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     linux-kernel@...r.kernel.org,
        Nianyao Tang <tangnianyao@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] irqchip/gic-v4: Fix non-stick page size error for setup
 GITS_BASER

Hi Shaokun,

On 2020-03-16 05:48, Shaokun Zhang wrote:
> Hi Marc，
> 
> On 2020/3/13 20:00, Marc Zyngier wrote:
>> Shaokun, Nianyao,
>> 
>> On 2020-03-13 08:46, Shaokun Zhang wrote:
>>> From: Nianyao Tang <tangnianyao@...wei.com>
>>> 
>>> There is an error when ITS is probed if hw GITS_BASER<2>
>>> only supports psz=SZ_16K while GITS_BASER<1> only supports psz=SZ_4K.
>>> In its_alloc_tables, it has updated GITS_BASER<1>.psz and uses
>>> psz=SZ_4K for setup GITS_BASER<2>, and would fail in writing
>>> GITS_BASER<2>.psz=SZ_4K. 4K PAGE is the smallest and shall stop retry
>>> for other page sizes.
>>> 
>>> That latter GITS_BASER<n>.psz is larger than former, will lead
>>> to similar error.
>>> 
>>> [    0.000000] ITS@...000000660000000: Virtual CPUs doesn't stick:
>>> ba1f0824404004ff ba1f0824404005ff
>>> [    0.000000] ITS@...000000660000000: failed probing (-6)
>>> [    0.000000] ITS: No ITS available, not enabling LPIs
>>> 
>>> From GIC SPEC document, it's allowed for this implematation, the 
>>> latter
>>> GITS_BASER<n>.psz is larger than the former.
>> 
>> I was really hoping nobody would build an ITS with disjoint sets of
>> page sizes. Oh well...
>> 
>>> Let's fix this error with following patch.
>>> 
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: Marc Zyngier <maz@...nel.org>
>>> Signed-off-by: Nianyao Tang <tangnianyao@...wei.com>
>>> Signed-off-by: Shaokun Zhang <zhangshaokun@...ilicon.com>
>>> ---
>>>  drivers/irqchip/irq-gic-v3-its.c | 1 -
>>>  1 file changed, 1 deletion(-)
>>> 
>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
>>> b/drivers/irqchip/irq-gic-v3-its.c
>>> index 83b1186..59bf8d6 100644
>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>> @@ -2341,7 +2341,6 @@ static int its_alloc_tables(struct its_node 
>>> *its)
>>>          }
>>> 
>>>          /* Update settings which will be used for next BASERn */
>>> -        psz = baser->psz;
>>>          cache = baser->val & GITS_BASER_CACHEABILITY_MASK;
>>>          shr = baser->val & GITS_BASER_SHAREABILITY_MASK;
>>>      }
>> 
>> I think this just papers over the problem, and I'd rather tackle it 
>> fully
>> by forcing the probe of the supported page sizes for each GITS_BASERn
>> register. See the patch below (which I've only boot-tested once on 
>> pretty
>> standard HW as well as a guest).
>> 
>> This, in turn, simplifies the way we perform the allocation (no nested
>> retry loop). This is of course a much more patch invasive, but at 
>> least
>> it doesn't leave too much cruft behind.
>> 
>> Please let me know whether this solves your issue.
>> 
> 
> Thanks your quick reply.
> With your following fixed patch, it can work for Nianyao, So:
> Tested-by: Nianyao Tang <tangnianyao@...wei.com>

Thanks for the quick feedback. I've now added this patch to the 5.7 
queue.

         M.
-- 
Jazz is not dead. It just smells funny...