riscv/mp_machdep.c: Flush the TLB after releasing APs

Spurious page faults caused by cached invalid entries may occur when
starting APs and potentially panic the kernel if we're running in
a non-sleepable context.

Fix this avoidable panic by flushing the TLB after the AP is released.

Differential Revision:	https://reviews.freebsd.org/D57003
Reviewed by:	markj

1 files changed, 5 insertions, 0 deletions

diff --git a/sys/riscv/riscv/mp_machdep.c b/sys/riscv/riscv/mp_machdep.c
index 235bee15ca29..9c81d9ee1043 100644
--- a/sys/riscv/riscv/mp_machdep.c
+++ b/sys/riscv/riscv/mp_machdep.c
@@ -172,6 +172,11 @@ init_secondary(uint64_t hart)
 	while (!atomic_load_int(&aps_ready))
 		__asm __volatile("wfi");
 
+	/*
+	 * Flush the TLB to avoid spurious kernel page faults
+	 * on implementations that cache invalid entries.
+	 */
+	sfence_vma();
 	/* Initialize curthread */
 	KASSERT(PCPU_GET(idlethread) != NULL, ("no idle thread"));
 	pcpup->pc_curthread = pcpup->pc_idlethread;