Subject: [PATCH 2/3] powerpc/watchpoint: Disable pagefaults when getting user instruction

From: Benjamin Gray <[email-masked]>
Date: Tue, 29 Aug 2023 16:34:56 +1000

This is called in an atomic context, so is not allowed to sleep if a
user page needs to be faulted in and has nowhere it can be deferred to.
The pagefault_disabled() function is documented as preventing user
access methods from sleeping.

In practice the page will be mapped in nearly always because we are
reading the instruction that just triggered the watchpoint trap.

Signed-off-by: Benjamin Gray <[email-masked]>
---
 arch/powerpc/kernel/hw_breakpoint_constraints.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/hw_breakpoint_constraints.c b/arch/powerpc/kernel/hw_breakpoint_constraints.c
index a74623025f3a..9e51801c4915 100644
--- a/arch/powerpc/kernel/hw_breakpoint_constraints.c
+++ b/arch/powerpc/kernel/hw_breakpoint_constraints.c
@@ -131,8 +131,13 @@ void wp_get_instr_detail(struct pt_regs *regs, ppc_inst_t *instr,
 			 int *type, int *size, unsigned long *ea)
 {
 	struct instruction_op op;
+	int err;
 
-	if (__get_user_instr(*instr, (void __user *)regs->nip))
+	pagefault_disable();
+	err = __get_user_instr(*instr, (void __user *)regs->nip);
+	pagefault_enable();
+
+	if (err)
 		return;
 
 	analyse_instr(&op, regs, *instr);
-- 
2.41.0