arm64: Do not attempt to use init_mm in reset_context()

commit 565630d503ef24e44c252bed55571b3a0d68455f upstream.

After secondary CPU boot or hotplug, the active_mm of the idle thread is
&init_mm. The init_mm.pgd (swapper_pg_dir) is only meant for TTBR1_EL1
and must not be set in TTBR0_EL1. Since when active_mm == &init_mm the
TTBR0_EL1 is already set to the reserved value, there is no need to
perform any context reset.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index baa758d37021..76c1e6cd36fc 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -92,6 +92,14 @@ static void reset_context(void *info)
         unsigned int cpu = smp_processor_id();
         struct mm_struct *mm = current->active_mm;
 
+        /*
+         * current->active_mm could be init_mm for the idle thread immediately
+         * after secondary CPU boot or hotplug. TTBR0_EL1 is already set to
+         * the reserved value, so no need to reset any context.
+         */
+        if (mm == &init_mm)
+                return;
+
         smp_rmb();
         asid = cpu_last_asid + cpu;