Re: [PATCH v5 11/23] irqchip/gic-v4.1: Plumb get/set_irqchip_state SGI callbacks

Auger Eric
2020-03-16T21:43:32Z

Hi Marc,

On 3/4/20 9:33 PM, 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
emitting
> "clear" bit set.
>
> This requires some interesting locking though:
> - When talking to the redistributor, we must make sure that the VPE
> affinity doesn't change, hence taking the VPE lock.
> - At the same time, we must ensure that nobody accesses the same
> redistributor's GICR_VSGI*R registers for a different VPE, which
GICR_VSGIR
> would corrupt the reading of the pending bits. We thus take the
> per-RD spinlock. Much fun.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> drivers/irqchip/irq-gic-v3-its.c | 73 ++++++++++++++++++++++++++++++
> include/linux/irqchip/arm-gic-v3.h | 14 ++++++
> 2 files changed, 87 insertions(+)
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index c93f178914ee..fb2b836c31ff 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -3962,11 +3962,84 @@ 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;
> + unsigned long flags;
> + u32 count = 1000000; /* 1s! */
where does it come from? I did not find any info in the spec about this
delay.
> + u32 status;
> + int cpu;
> +
> + if (which != IRQCHIP_STATE_PENDING)
> + return -EINVAL;
> +
> + /*
> + * Locking galore! We can race against two different events:
> + *
> + * - Concurent vPE affinity change: we must make sure it cannot
> + * happen, or we'll talk to the wrong redistributor. This is
> + * identical to what happens with vLPIs.
> + *
> + * - Concurrent VSGIPENDR access: As it involves accessing two
> + * MMIO registers, this must be made atomic one way or another.
> + */
> + cpu = vpe_to_cpuid_lock(vpe, &flags);
> + raw_spin_lock(&gic_data_rdist_cpu(cpu)->rd_lock);
> + base = gic_data_rdist_cpu(cpu)->rd_base + SZ_128K;
> + 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:
> + raw_spin_unlock(&gic_data_rdist_cpu(cpu)->rd_lock);
> + vpe_to_cpuid_unlock(vpe, flags);
> + *val = !!(status & (1 << d->hwirq));
> +
> + return 0;
cascade an error on timeout?
> +}
> +
> 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 fd3be49ac9a5..830d2abf14b3 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)
as spotted by Zenghui 3, 0
> +
> #define GITS_CTLR_ENABLE (1U << 0)
> #define GITS_CTLR_ImDe (1U << 1)
> #define GITS_CTLR_ITS_NUMBER_SHIFT 4
>

Thanks

Eric