[PATCH v2 03/10] irqchip/gic-v5: Serialise IRS synchronisation requests

[Sascha Bischoff <sascha.bischoff@arm.com>]

IRS_SYNCR writes are ignored while IRS_SYNC_STATUSR.IDLE is clear.
Calls to gicv5_irs_syncr() for different IRQs can overlap, allowing
the second request to be dropped. Its caller can then observe the
first request completing and assume that its own events have been
processed.

With GICv5 ITS KVM support, gicv5_irs_syncr() is also called while
restoring the host ITTE in gicv5_its_set_vcpu_affinity(). The callback
runs under the IRQ descriptor lock via irq_set_vcpu_affinity(), so it
cannot sleep.

Serialise the request and completion poll with a raw spinlock, and use
atomic polling because the synchronisation runs while holding the IRQ
descriptor lock.

Fixes: 57d72196dfc8 ("irqchip/gic-v5: Add GICv5 ITS support")
Cc: stable@vger.kernel.org
Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
---
 drivers/irqchip/irq-gic-v5-irs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v5-irs.c b/drivers/irqchip/irq-gic-v5-irs.c
index 4edf787f3f97f..ead76560ea08f 100644
--- a/drivers/irqchip/irq-gic-v5-irs.c
+++ b/drivers/irqchip/irq-gic-v5-irs.c
@@ -10,6 +10,7 @@
 #include <linux/log2.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/spinlock.h>
 
 #include <linux/irqchip.h>
 #include <linux/irqchip/arm-gic-v5.h>
@@ -22,6 +23,8 @@
 #define LPI_ID_BITS_LINEAR		12
 
 static DEFINE_PER_CPU_READ_MOSTLY(struct gicv5_irs_chip_data *, per_cpu_irs_data);
+/* Synchronization requests must not overlap in an IRS Domain. */
+static DEFINE_RAW_SPINLOCK(irs_sync_lock);
 static LIST_HEAD(irs_nodes);
 
 static u32 irs_readl_relaxed(struct gicv5_irs_chip_data *irs_data,
@@ -507,10 +510,11 @@ void gicv5_irs_syncr(void)
 		return;
 
 	syncr = FIELD_PREP(GICV5_IRS_SYNCR_SYNC, 1);
+	guard(raw_spinlock_irqsave)(&irs_sync_lock);
 	irs_writel_relaxed(irs_data, syncr, GICV5_IRS_SYNCR);
 
-	gicv5_wait_for_op(irs_data->irs_base, GICV5_IRS_SYNC_STATUSR,
-			  GICV5_IRS_SYNC_STATUSR_IDLE);
+	gicv5_wait_for_op_atomic(irs_data->irs_base, GICV5_IRS_SYNC_STATUSR,
+				 GICV5_IRS_SYNC_STATUSR_IDLE, NULL);
 }
 
 int gicv5_irs_register_cpu(int cpuid)

-- 
2.34.1