POR_EL1 is about to be used by the kpkeys framework, modifying it
for (typically small) sections of code. If an exception occurs
during that window and scheduling occurs, we must ensure that
POR_EL1 is context-switched as needed (saving the old value and
restoring the new one). An ISB is needed to ensure the write takes
effect, so we skip it if the new value is the same as the old, like
for POR_EL0.

Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Linu Cherian <linu.cherian@arm.com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 arch/arm64/include/asm/processor.h |  1 +
 arch/arm64/kernel/process.c        | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 481f1999f7c1..18424d91d8b2 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -195,6 +195,7 @@ struct thread_struct {
 	u64			svcr;
 	u64			tpidr2_el0;
 	u64			por_el0;
+	u64			por_el1;
 #ifdef CONFIG_ARM64_GCS
 	unsigned int		gcs_el0_mode;
 	unsigned int		gcs_el0_locked;
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 42b15b0c069f..a3984aedfebe 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -51,6 +51,7 @@
 #include <asm/exec.h>
 #include <asm/fpsimd.h>
 #include <asm/gcs.h>
+#include <asm/kpkeys.h>
 #include <asm/mmu_context.h>
 #include <asm/mpam.h>
 #include <asm/mte.h>
@@ -446,6 +447,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
 	ptrauth_thread_init_kernel(p);
 
+	if (system_supports_poe())
+		p->thread.por_el1 = POR_EL1_INIT;
+
 	if (likely(!args->fn)) {
 		*childregs = *current_pt_regs();
 		childregs->regs[0] = 0;
@@ -698,6 +702,12 @@ static void permission_overlay_switch(struct task_struct *next)
 		 * of POR_EL0.
 		 */
 	}
+
+	current->thread.por_el1 = read_sysreg_s(SYS_POR_EL1);
+	if (current->thread.por_el1 != next->thread.por_el1) {
+		write_sysreg_s(next->thread.por_el1, SYS_POR_EL1);
+		isb();
+	}
 }
 
 /*

-- 
2.56.0