RISC-V: Allow marking IPIs as suitable for remote FENCEs

To do remote FENCEs (i.e. remote TLB flushes) using IPI calls on
Linux RISC-V, we need hardware mechanism to directly inject IPI
from kernel instead of using SBI calls.

The upcoming ACLINT [M|S]SWI devices and AIA IMSIC devices allow
direct IPI injection from kernel. To support this, we extend the
riscv_ipi_set_virq_range() function so that irqchip drivers can
mark IPIs as suitable for remote FENCEs.

Signed-off-by: Anup Patel <anup.patel@wdc.com>

arch/riscv/include/asm/smp.h

@@ -16,6 +16,9 @@ struct seq_file;
 extern unsigned long boot_cpu_hartid;
 
 #ifdef CONFIG_SMP
+
+#include <linux/jump_label.h>
+
 /*
  * Mapping between linux logical cpu index and hartid.
  */
@@ -47,7 +50,12 @@ void riscv_ipi_disable(void);
 void riscv_ipi_setup(void);
 
 /* Set the IPI interrupt numbers for arch (called by irqchip drivers) */
-void riscv_ipi_set_virq_range(int virq, int nr_irqs);
+void riscv_ipi_set_virq_range(int virq, int nr_irqs, bool use_for_rfence);
+
+/* Check if we can use IPIs for remote FENCEs */
+DECLARE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
+#define riscv_use_ipi_for_rfence() \
+	static_branch_unlikely(&riscv_ipi_for_rfence)
 
 /* Secondary hart entry */
 asmlinkage void smp_callin(void);
@@ -106,6 +114,11 @@ static inline void riscv_ipi_set_virq_range(int virq, int nr)
 {
 }
 
+static inline bool riscv_use_ipi_for_rfence(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_SMP */
 
 #if defined(CONFIG_HOTPLUG_CPU) && (CONFIG_SMP)

arch/riscv/kernel/sbi-ipi.c

@@ -153,7 +153,7 @@ static int __init sbi_ipi_set_virq(void)
 		return -ENOMEM;
 	}
 
-	riscv_ipi_set_virq_range(virq, BITS_PER_LONG);
+	riscv_ipi_set_virq_range(virq, BITS_PER_LONG, false);
 
 	return 0;
 }

arch/riscv/kernel/smp.c

@@ -178,14 +178,21 @@ void riscv_ipi_setup(void)
 	riscv_ipi_enable();
 }
 
-void riscv_ipi_set_virq_range(int virq, int nr)
+DEFINE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
+EXPORT_SYMBOL_GPL(riscv_ipi_for_rfence);
+
+void riscv_ipi_set_virq_range(int virq, int nr, bool use_for_rfence)
 {
 	if (WARN_ON(ipi_virq_base))
 		return;
 
 	WARN_ON(nr < IPI_MAX);
 	nr_ipi = min(nr, IPI_MAX);
 	ipi_virq_base = virq;
+	if (use_for_rfence)
+		static_branch_enable(&riscv_ipi_for_rfence);
+	else
+		static_branch_disable(&riscv_ipi_for_rfence);
 }
 EXPORT_SYMBOL_GPL(riscv_ipi_set_virq_range);