Subject: Re: [PATCH v4 08/20] irqchip/gic-v4.1: Plumb get/set_irqchip_state SGI callbacks

From: Marc Zyngier <[email-masked]>
Date: Tue, 18 Feb 2020 09:27:44 +0000

Hi Zenghui,

On 2020-02-18 07:00, Zenghui Yu wrote:
> Hi Marc,
> 
> On 2020/2/14 22:57, Marc Zyngier wrote:
>> To implement the get/set_irqchip_state callbacks (limited to the
>> PENDING state), we have to use a particular set of hacks:
>> 
>> - Reading the pending state is done by using a pair of new 
>> redistributor
>>    registers (GICR_VSGIR, GICR_VSGIPENDR), which allow the 16 
>> interrupts
>>    state to be retrieved.
>> - Setting the pending state is done by generating it as we'd otherwise 
>> do
>>    for a guest (writing to GITS_SGIR)
>> - Clearing the pending state is done by emiting a VSGI command with 
>> the
>>    "clear" bit set.
>> 
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>   drivers/irqchip/irq-gic-v3-its.c   | 56 
>> ++++++++++++++++++++++++++++++
>>   include/linux/irqchip/arm-gic-v3.h | 14 ++++++++
>>   2 files changed, 70 insertions(+)
>> 
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
>> b/drivers/irqchip/irq-gic-v3-its.c
>> index 1e448d9a16ea..a9753435c4ff 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -3915,11 +3915,67 @@ static int its_sgi_set_affinity(struct 
>> irq_data *d,
>>   	return -EINVAL;
>>   }
>>   +static int its_sgi_set_irqchip_state(struct irq_data *d,
>> +				     enum irqchip_irq_state which,
>> +				     bool state)
>> +{
>> +	if (which != IRQCHIP_STATE_PENDING)
>> +		return -EINVAL;
>> +
>> +	if (state) {
>> +		struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
>> +		struct its_node *its = find_4_1_its();
>> +		u64 val;
>> +
>> +		val  = FIELD_PREP(GITS_SGIR_VPEID, vpe->vpe_id);
>> +		val |= FIELD_PREP(GITS_SGIR_VINTID, d->hwirq);
>> +		writeq_relaxed(val, its->sgir_base + GITS_SGIR - SZ_128K);
>> +	} else {
>> +		its_configure_sgi(d, true);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int its_sgi_get_irqchip_state(struct irq_data *d,
>> +				     enum irqchip_irq_state which, bool *val)
>> +{
>> +	struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
>> +	void __iomem *base = gic_data_rdist_cpu(vpe->col_idx)->rd_base + 
>> SZ_128K;
> 
> There might be a race on reading the 'vpe->col_idx' against a 
> concurrent
> vPE schedule (col_idx will be modified in its_vpe_set_affinity)? Will 
> we
> end up accessing the GICR_VSGI* registers of the old redistributor,
> while the vPE is now resident on the new one? Or is it harmful?

Very well spotted. There is a potential problem if old and new RDs are 
not part
of the same CommonLPIAff group.

> The same question for direct_lpi_inv(), where 'vpe->col_idx' will be
> used in irq_to_cpuid().

Same problem indeed. We need to ensure that no VMOVP operation can occur 
whilst
we use col_idx to access a redistributor. This means a vPE lock of some 
sort
that will protect the affinity.

But I think there is a slightly more general problem here, which we 
failed to
see initially: the same issue exists for physical LPIs, as col_map[] can 
be
updated (its_set_affinity()) in parallel with a direct invalidate.

The good old invalidation through the ITS does guarantee that the two 
operation
don't overlap, but direct invalidation breaks it.

Let me have a think about it.

> 
>> +	u32 count = 1000000;	/* 1s! */
>> +	u32 status;
>> +
>> +	if (which != IRQCHIP_STATE_PENDING)
>> +		return -EINVAL;
>> +
>> +	writel_relaxed(vpe->vpe_id, base + GICR_VSGIR);
>> +	do {
>> +		status = readl_relaxed(base + GICR_VSGIPENDR);
>> +		if (!(status & GICR_VSGIPENDR_BUSY))
>> +			goto out;
>> +
>> +		count--;
>> +		if (!count) {
>> +			pr_err_ratelimited("Unable to get SGI status\n");
>> +			goto out;
>> +		}
>> +		cpu_relax();
>> +		udelay(1);
>> +	} while(count);
>> +
>> +out:
>> +	*val = !!(status & (1 << d->hwirq));
>> +
>> +	return 0;
>> +}
>> +
>>   static struct irq_chip its_sgi_irq_chip = {
>>   	.name			= "GICv4.1-sgi",
>>   	.irq_mask		= its_sgi_mask_irq,
>>   	.irq_unmask		= its_sgi_unmask_irq,
>>   	.irq_set_affinity	= its_sgi_set_affinity,
>> +	.irq_set_irqchip_state	= its_sgi_set_irqchip_state,
>> +	.irq_get_irqchip_state	= its_sgi_get_irqchip_state,
>>   };
>>     static int its_sgi_irq_domain_alloc(struct irq_domain *domain,
>> diff --git a/include/linux/irqchip/arm-gic-v3.h 
>> b/include/linux/irqchip/arm-gic-v3.h
>> index a89578884263..64da945486ac 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -345,6 +345,15 @@
>>   #define GICR_VPENDBASER_4_1_VGRP1EN	(1ULL << 58)
>>   #define GICR_VPENDBASER_4_1_VPEID	GENMASK_ULL(15, 0)
>>   +#define GICR_VSGIR			0x0080
>> +
>> +#define GICR_VSGIR_VPEID		GENMASK(15, 0)
>> +
>> +#define GICR_VSGIPENDR			0x0088
>> +
>> +#define GICR_VSGIPENDR_BUSY		(1U << 31)
>> +#define GICR_VSGIPENDR_PENDING		GENMASK(15, 0)
>> +
>>   /*
>>    * ITS registers, offsets from ITS_base
>>    */
>> @@ -368,6 +377,11 @@
>>     #define GITS_TRANSLATER			0x10040
>>   +#define GITS_SGIR			0x20020
>> +
>> +#define GITS_SGIR_VPEID			GENMASK_ULL(47, 32)
>> +#define GITS_SGIR_VINTID		GENMASK_ULL(7, 0)
> 
> The spec says vINTID field is [3:0] of the GITS_SGIR.

Indeed, well spotted again!

Thanks,

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

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