From 8ada8f11928b1b5b96fc7b349cc6c3e97be546ed Mon Sep 17 00:00:00 2001
From: James Morse <james.morse@arm.com>
Date: Wed, 4 May 2022 17:29:38 +0100
Subject: [PATCH] FIXME arm_mpam: Make mpam_msmon_read() safe for irq-masked
callers
The resctrl_pmu driver calls resctrl_arch_rmid_read() from interrupt
context. This eventually ends up in mpam_msmon_read() which cross-calls
to access remote cache-slices, and sleeps if the monitor returned
not-ready.
To support resctrl_pmu, remove these behaviours if irqs are masked.
Instead of cross-calling, return an error. This means the resctrl_pmu
can't be supported on platforms with cache-slices that aren't accessible
from every CPU. Instead of sleeping when the counter is busy, return
-EBUSY. The resctrl_pmu driver will not update the counter in this case.
Signed-off-by: James Morse <james.morse@arm.com>
---
drivers/platform/mpam/mpam_devices.c | 31 +++++++++++++++++++---------
1 file changed, 21 insertions(+), 10 deletions(-)
diff --git a/drivers/platform/mpam/mpam_devices.c b/drivers/platform/mpam/mpam_devices.c
index 433a3e34b92bd..31edaeee86ee7 100644
--- a/drivers/platform/mpam/mpam_devices.c
+++ b/drivers/platform/mpam/mpam_devices.c
@@ -935,8 +935,6 @@ static void __ris_msmon_read(void *arg)
struct msmon_mbwu_state *mbwu_state;
u32 mon_sel, ctl_val, flt_val, cur_ctl, cur_flt;
- lockdep_assert_held(&msc->lock);
-
spin_lock_irqsave(&msc->mon_sel_lock, flags);
mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
@@ -1015,9 +1013,11 @@ static void __ris_msmon_read(void *arg)
*(m->val) += now;
}
+/* This is also called in atomic context via the restrl_pmu driver */
static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)
{
- int err, idx;
+ int err, idx, cpu;
+ struct cpumask *mask;
struct mpam_msc *msc;
struct mpam_msc_ris *ris;
@@ -1026,10 +1026,23 @@ static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)
arg->ris = ris;
msc = ris->msc;
- mutex_lock(&msc->lock);
- err = smp_call_function_any(&msc->accessibility,
- __ris_msmon_read, arg, true);
- mutex_unlock(&msc->lock);
+ mask = &msc->accessibility;
+
+ /*
+ * Fail the access if we need to cross call to reach this MSC
+ * and irqs are masked. The PMU driver calls this with irqs
+ * masked, but it also specifies where the callback should run.
+ */
+ err = -EIO;
+ cpu = get_cpu();
+ if (cpumask_test_cpu(cpu, mask)) {
+ __ris_msmon_read(arg);
+ err = 0;
+ } else if (!irqs_disabled())
+ err = smp_call_function_any(mask, __ris_msmon_read,
+ arg, true);
+ put_cpu();
+
if (!err && arg->err)
err = arg->err;
if (err)
@@ -1048,8 +1061,6 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
u64 wait_jiffies = 0;
struct mpam_props *cprops = &comp->class->props;
- might_sleep();
-
if (!mpam_is_enabled())
return -EIO;
@@ -1063,7 +1074,7 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
*val = 0;
err = _msmon_read(comp, &arg);
- if (err == -EBUSY)
+ if (err == -EBUSY && !irqs_disabled())
wait_jiffies = usecs_to_jiffies(comp->class->nrdy_usec);
while (wait_jiffies)
--
GitLab