irqchip/gic-v3-its: Limit memreserve cpuhp state lifetime

The new memreserve cpuhp callback only needs to survive up until a point
where every CPU in the system has booted once. Beyond that, it becomes a
no-op and can be put in the bin.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211027151506.2085066-4-valentin.schneider@arm.com

drivers/irqchip/irq-gic-v3-its.c

@@ -5203,6 +5203,15 @@ int its_cpu_init(void)
 	return 0;
 }
 
+static void rdist_memreserve_cpuhp_cleanup_workfn(struct work_struct *work)
+{
+	cpuhp_remove_state_nocalls(gic_rdists->cpuhp_memreserve_state);
+	gic_rdists->cpuhp_memreserve_state = CPUHP_INVALID;
+}
+
+static DECLARE_WORK(rdist_memreserve_cpuhp_cleanup_work,
+		    rdist_memreserve_cpuhp_cleanup_workfn);
+
 static int its_cpu_memreserve_lpi(unsigned int cpu)
 {
 	struct page *pend_page;
@@ -5231,6 +5240,10 @@ static int its_cpu_memreserve_lpi(unsigned int cpu)
 	}
 
 out:
+	/* Last CPU being brought up gets to issue the cleanup */
+	if (cpumask_equal(&cpus_booted_once_mask, cpu_possible_mask))
+		schedule_work(&rdist_memreserve_cpuhp_cleanup_work);
+
 	gic_data_rdist()->flags |= RD_LOCAL_MEMRESERVE_DONE;
 	return ret;
 }
@@ -5425,6 +5438,7 @@ int __init its_lpi_memreserve_init(void)
 	if (!efi_enabled(EFI_CONFIG_TABLES))
 		return 0;
 
+	gic_rdists->cpuhp_memreserve_state = CPUHP_INVALID;
 	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				  "irqchip/arm/gicv3/memreserve:online",
 				  its_cpu_memreserve_lpi,
@@ -5432,6 +5446,8 @@ int __init its_lpi_memreserve_init(void)
 	if (state < 0)
 		return state;
 
+	gic_rdists->cpuhp_memreserve_state = state;
+
 	return 0;
 }
 

include/linux/irqchip/arm-gic-v3.h

@@ -624,6 +624,7 @@ struct rdists {
 	u64			flags;
 	u32			gicd_typer;
 	u32			gicd_typer2;
+	int                     cpuhp_memreserve_state;
 	bool			has_vlpis;
 	bool			has_rvpeid;
 	bool			has_direct_lpi;