linux-kernel - Re: [PATCH 10/35] irqchip/gic-v4.1: VPE table (aka GICR

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Date:   Wed, 25 Sep 2019 18:14:46 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-kernel@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH 10/35] irqchip/gic-v4.1: VPE table (aka  GICR_VPROPBASER) allocation

On 2019-09-25 15:41, Marc Zyngier wrote:
> On 25/09/2019 14:04, Zenghui Yu wrote:
>> Hi Marc,
>>
>> Some questions about this patch, mostly to confirm that I would
>> understand things here correctly.
>>
>> On 2019/9/24 2:25, Marc Zyngier wrote:
>>> GICv4.1 defines a new VPE table that is potentially shared between
>>> both the ITSs and the redistributors, following complicated 
>>> affinity
>>> rules.
>>>
>>> To make things more confusing, the programming of this table at
>>> the redistributor level is reusing the GICv4.0 GICR_VPROPBASER 
>>> register
>>> for something completely different.
>>>
>>> The code flow is somewhat complexified by the need to respect the
>>> affinities required by the HW, meaning that tables can either be
>>> inherited from a previously discovered ITS or redistributor.
>>>
>>> Signed-off-by: Marc Zyngier <maz@...nel.org>
>>> ---
>>
>> [...]
>>
>>> @@ -1962,6 +1965,65 @@ static bool its_parse_indirect_baser(struct 
>>> its_node *its,
>>>   	return indirect;
>>>   }
>>>
>>> +static u32 compute_common_aff(u64 val)
>>> +{
>>> +	u32 aff, clpiaff;
>>> +
>>> +	aff = FIELD_GET(GICR_TYPER_AFFINITY, val);
>>> +	clpiaff = FIELD_GET(GICR_TYPER_COMMON_LPI_AFF, val);
>>> +
>>> +	return aff & ~(GENMASK(31, 0) >> (clpiaff * 8));
>>> +}
>>> +
>>> +static u32 compute_its_aff(struct its_node *its)
>>> +{
>>> +	u64 val;
>>> +	u32 svpet;
>>> +
>>> +	/*
>>> +	 * Reencode the ITS SVPET and MPIDR as a GICR_TYPER, and compute
>>> +	 * the resulting affinity. We then use that to see if this match
>>> +	 * our own affinity.
>>> +	 */
>>> +	svpet = FIELD_GET(GITS_TYPER_SVPET, its->typer);
>>> +	val  = FIELD_PREP(GICR_TYPER_COMMON_LPI_AFF, svpet);
>>> +	val |= FIELD_PREP(GICR_TYPER_AFFINITY, its->mpidr);
>>> +	return compute_common_aff(val);
>>> +}
>>> +
>>> +static struct its_node *find_sibbling_its(struct its_node 
>>> *cur_its)
>>> +{
>>> +	struct its_node *its;
>>> +	u32 aff;
>>> +
>>> +	if (!FIELD_GET(GITS_TYPER_SVPET, cur_its->typer))
>>> +		return NULL;
>>> +
>>> +	aff = compute_its_aff(cur_its);
>>> +
>>> +	list_for_each_entry(its, &its_nodes, entry) {
>>> +		u64 baser;
>>> +
>>> +		if (!is_v4_1(its) || its == cur_its)
>>> +			continue;
>>> +
>>> +		if (!FIELD_GET(GITS_TYPER_SVPET, its->typer))
>>> +			continue;
>>> +
>>> +		if (aff != compute_its_aff(its))
>>> +			continue;
>>> +
>>> +		/* GICv4.1 guarantees that the vPE table is GITS_BASER2 */
>>> +		baser = its->tables[2].val;
>>> +		if (!(baser & GITS_BASER_VALID))
>>> +			continue;
>>> +
>>> +		return its;
>>> +	}
>>> +
>>> +	return NULL;
>>> +}
>>> +
>>>   static void its_free_tables(struct its_node *its)
>>>   {
>>>   	int i;
>>> @@ -2004,6 +2066,15 @@ static int its_alloc_tables(struct its_node 
>>> *its)
>>>   			break;
>>>
>>>   		case GITS_BASER_TYPE_VCPU:
>>> +			if (is_v4_1(its)) {
>>> +				struct its_node *sibbling;
>>> +
>>> +				if ((sibbling = find_sibbling_its(its))) {
>>> +					its->tables[2] = sibbling->tables[2];
>>
>> This means thst the vPE table is shared between ITSs which are under 
>> the
>> same affinity group?
>
> That's indeed what this is trying to do...
>
>> Don't we need to set GITS_BASER (by its_setup_baser()) here to tell 
>> this
>> ITS where the vPE table lacates?
>
> Absolutely. This is a bug. I didn't spot it as my model only has a
> single ITS.

FWIW, I've pushed out an updated branch with this fixed as well as the 
rest of the comments you had.

Thanks again,

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