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

From: Marc Zyngier
Date: Tue Feb 18 2020 - 10:31:08 EST

Hi Zenghui,

On 2020-02-18 09:27, Marc Zyngier wrote:
Hi Zenghui,

On 2020-02-18 07:00, Zenghui Yu wrote:
Hi Marc,

[...]

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.

So I've thought about it, wrote a patch, and I don't really like the look of it.
This is pretty invasive, and we end-up serializing a lot more than we used to
(the repurposing of vlpi_lock to a general "lpi mapping lock" is probably too
coarse).

It of course needs splitting over at least three patches, but it'd be good if
you could have a look (applies on top of the whole series).

Thanks,

M.

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 7656b353a95f..0ed286dba827 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -144,7 +144,7 @@ struct event_lpi_map {
u16 *col_map;
irq_hw_number_t lpi_base;
int nr_lpis;
- raw_spinlock_t vlpi_lock;
+ raw_spinlock_t map_lock;
struct its_vm *vm;
struct its_vlpi_map *vlpi_maps;
int nr_vlpis;
@@ -240,15 +240,33 @@ static struct its_vlpi_map *get_vlpi_map(struct irq_data *d)
return NULL;
}

-static int irq_to_cpuid(struct irq_data *d)
+static int irq_to_cpuid_lock(struct irq_data *d, unsigned long *flags)
{
- struct its_device *its_dev = irq_data_get_irq_chip_data(d);
struct its_vlpi_map *map = get_vlpi_map(d);
+ int cpu;

- if (map)
- return map->vpe->col_idx;
+ if (map) {
+ raw_spin_lock_irqsave(&map->vpe->vpe_lock, *flags);
+ cpu = map->vpe->col_idx;
+ } else {
+ struct its_device *its_dev = irq_data_get_irq_chip_data(d);
+ raw_spin_lock_irqsave(&its_dev->event_map.map_lock, *flags);
+ cpu = its_dev->event_map.col_map[its_get_event_id(d)];
+ }

- return its_dev->event_map.col_map[its_get_event_id(d)];
+ return cpu;
+}
+
+static void irq_to_cpuid_unlock(struct irq_data *d, unsigned long flags)
+{
+ struct its_vlpi_map *map = get_vlpi_map(d);
+
+ if (map) {
+ raw_spin_unlock_irqrestore(&map->vpe->vpe_lock, flags);
+ } else {
+ struct its_device *its_dev = irq_data_get_irq_chip_data(d);
+ raw_spin_unlock_irqrestore(&its_dev->event_map.map_lock, flags);
+ }
}

static struct its_collection *valid_col(struct its_collection *col)
@@ -1384,6 +1402,8 @@ static void direct_lpi_inv(struct irq_data *d)
{
struct its_vlpi_map *map = get_vlpi_map(d);
void __iomem *rdbase;
+ unsigned long flags;
+ int cpu;
u64 val;

if (map) {
@@ -1399,10 +1419,12 @@ static void direct_lpi_inv(struct irq_data *d)
}

/* Target the redistributor this LPI is currently routed to */
- rdbase = per_cpu_ptr(gic_rdists->rdist, irq_to_cpuid(d))->rd_base;
+ cpu = irq_to_cpuid_lock(d, &flags);
+ rdbase = per_cpu_ptr(gic_rdists->rdist, cpu)->rd_base;
gic_write_lpir(val, rdbase + GICR_INVLPIR);

wait_for_syncr(rdbase);
+ irq_to_cpuid_unlock(d, flags);
}

static void lpi_update_config(struct irq_data *d, u8 clr, u8 set)
@@ -1471,11 +1493,11 @@ static void its_unmask_irq(struct irq_data *d)
static int its_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
bool force)
{
- unsigned int cpu;
const struct cpumask *cpu_mask = cpu_online_mask;
struct its_device *its_dev = irq_data_get_irq_chip_data(d);
struct its_collection *target_col;
- u32 id = its_get_event_id(d);
+ unsigned int from, cpu;
+ unsigned long flags;

/* A forwarded interrupt should use irq_set_vcpu_affinity */
if (irqd_is_forwarded_to_vcpu(d))
@@ -1496,12 +1518,16 @@ static int its_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
return -EINVAL;

/* don't set the affinity when the target cpu is same as current one */
- if (cpu != its_dev->event_map.col_map[id]) {
+ from = irq_to_cpuid_lock(d, &flags);
+ if (cpu != from) {
+ u32 id = its_get_event_id(d);
+
target_col = &its_dev->its->collections[cpu];
its_send_movi(its_dev, target_col, id);
its_dev->event_map.col_map[id] = cpu;
irq_data_update_effective_affinity(d, cpumask_of(cpu));
}
+ irq_to_cpuid_unlock(d, flags);

return IRQ_SET_MASK_OK_DONE;
}
@@ -1636,7 +1662,7 @@ static int its_vlpi_map(struct irq_data *d, struct its_cmd_info *info)
if (!info->map)
return -EINVAL;

- raw_spin_lock(&its_dev->event_map.vlpi_lock);
+ raw_spin_lock(&its_dev->event_map.map_lock);

if (!its_dev->event_map.vm) {
struct its_vlpi_map *maps;
@@ -1685,7 +1711,7 @@ static int its_vlpi_map(struct irq_data *d, struct its_cmd_info *info)
}

out:
- raw_spin_unlock(&its_dev->event_map.vlpi_lock);
+ raw_spin_unlock(&its_dev->event_map.map_lock);
return ret;
}

@@ -1695,7 +1721,7 @@ static int its_vlpi_get(struct irq_data *d, struct its_cmd_info *info)
struct its_vlpi_map *map;
int ret = 0;

- raw_spin_lock(&its_dev->event_map.vlpi_lock);
+ raw_spin_lock(&its_dev->event_map.map_lock);

map = get_vlpi_map(d);

@@ -1708,7 +1734,7 @@ static int its_vlpi_get(struct irq_data *d, struct its_cmd_info *info)
*info->map = *map;

out:
- raw_spin_unlock(&its_dev->event_map.vlpi_lock);
+ raw_spin_unlock(&its_dev->event_map.map_lock);
return ret;
}

@@ -1718,7 +1744,7 @@ static int its_vlpi_unmap(struct irq_data *d)
u32 event = its_get_event_id(d);
int ret = 0;

- raw_spin_lock(&its_dev->event_map.vlpi_lock);
+ raw_spin_lock(&its_dev->event_map.map_lock);

if (!its_dev->event_map.vm || !irqd_is_forwarded_to_vcpu(d)) {
ret = -EINVAL;
@@ -1748,7 +1774,7 @@ static int its_vlpi_unmap(struct irq_data *d)
}

out:
- raw_spin_unlock(&its_dev->event_map.vlpi_lock);
+ raw_spin_unlock(&its_dev->event_map.map_lock);
return ret;
}

@@ -3193,7 +3219,7 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
dev->event_map.col_map = col_map;
dev->event_map.lpi_base = lpi_base;
dev->event_map.nr_lpis = nr_lpis;
- raw_spin_lock_init(&dev->event_map.vlpi_lock);
+ raw_spin_lock_init(&dev->event_map.map_lock);
dev->device_id = dev_id;
INIT_LIST_HEAD(&dev->entry);

@@ -3560,6 +3586,7 @@ static int its_vpe_set_affinity(struct irq_data *d,
{
struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
int from, cpu = cpumask_first(mask_val);
+ unsigned long flags;

/*
* Changing affinity is mega expensive, so let's be as lazy as
@@ -3567,6 +3594,7 @@ static int its_vpe_set_affinity(struct irq_data *d,
* into the proxy device, we need to move the doorbell
* interrupt to its new location.
*/
+ raw_spin_lock_irqsave(&vpe->vpe_lock, flags);
if (vpe->col_idx == cpu)
goto out;

@@ -3586,6 +3614,7 @@ static int its_vpe_set_affinity(struct irq_data *d,

out:
irq_data_update_effective_affinity(d, cpumask_of(cpu));
+ raw_spin_unlock_irqrestore(&vpe->vpe_lock, flags);

return IRQ_SET_MASK_OK_DONE;
}
@@ -3695,11 +3724,15 @@ static void its_vpe_send_inv(struct irq_data *d)

if (gic_rdists->has_direct_lpi) {
void __iomem *rdbase;
+ unsigned long flags;
+ int cpu;

/* Target the redistributor this VPE is currently known on */
- rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
+ cpu = irq_to_cpuid_lock(d, &flags);
+ rdbase = per_cpu_ptr(gic_rdists->rdist, cpu)->rd_base;
gic_write_lpir(d->parent_data->hwirq, rdbase + GICR_INVLPIR);
wait_for_syncr(rdbase);
+ irq_to_cpuid_unlock(d, flags);
} else {
its_vpe_send_cmd(vpe, its_send_inv);
}
@@ -3735,14 +3768,18 @@ static int its_vpe_set_irqchip_state(struct irq_data *d,

if (gic_rdists->has_direct_lpi) {
void __iomem *rdbase;
+ unsigned long flags;
+ int cpu;

- rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
+ cpu = irq_to_cpuid_lock(d, &flags);
+ rdbase = per_cpu_ptr(gic_rdists->rdist, cpu)->rd_base;
if (state) {
gic_write_lpir(vpe->vpe_db_lpi, rdbase + GICR_SETLPIR);
} else {
gic_write_lpir(vpe->vpe_db_lpi, rdbase + GICR_CLRLPIR);
wait_for_syncr(rdbase);
}
+ irq_to_cpuid_unlock(d, flags);
} else {
if (state)
its_vpe_send_cmd(vpe, its_send_int);
@@ -3854,14 +3891,17 @@ static void its_vpe_4_1_deschedule(struct its_vpe *vpe,
static void its_vpe_4_1_invall(struct its_vpe *vpe)
{
void __iomem *rdbase;
+ unsigned long flags;
u64 val;

val = GICR_INVALLR_V;
val |= FIELD_PREP(GICR_INVALLR_VPEID, vpe->vpe_id);

/* Target the redistributor this vPE is currently known on */
+ raw_spin_lock_irqsave(&vpe->vpe_lock, flags);
rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
gic_write_lpir(val, rdbase + GICR_INVALLR);
+ raw_spin_unlock_irqrestore(&vpe->vpe_lock, flags);
}

static int its_vpe_4_1_set_vcpu_affinity(struct irq_data *d, void *vcpu_info)
@@ -3960,13 +4000,17 @@ 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;
+ void __iomem *base;
+ unsigned long flags;
u32 count = 1000000; /* 1s! */
u32 status;
+ int cpu;

if (which != IRQCHIP_STATE_PENDING)
return -EINVAL;

+ cpu = irq_to_cpuid_lock(d, &flags);
+ 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);
@@ -3983,6 +4027,7 @@ static int its_sgi_get_irqchip_state(struct irq_data *d,
} while(count);

out:
+ irq_to_cpuid_unlock(d, flags);
*val = !!(status & (1 << d->hwirq));

return 0;
@@ -4102,6 +4147,7 @@ static int its_vpe_init(struct its_vpe *vpe)
return -ENOMEM;
}

+ raw_spin_lock_init(&vpe->vpe_lock);
vpe->vpe_id = vpe_id;
vpe->vpt_page = vpt_page;
if (gic_rdists->has_rvpeid)
diff --git a/include/linux/irqchip/arm-gic-v4.h b/include/linux/irqchip/arm-gic-v4.h
index 46c167a6349f..fc43a63875a3 100644
--- a/include/linux/irqchip/arm-gic-v4.h
+++ b/include/linux/irqchip/arm-gic-v4.h
@@ -60,6 +60,7 @@ struct its_vpe {
};
};

+ raw_spinlock_t vpe_lock;
/*
* This collection ID is used to indirect the target
* redistributor for this VPE. The ID itself isn't involved in

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