powerpc/watchpoint: Disable pagefaults when getting user instruction

[ Upstream commit 3241f260eb830d27d09cc604690ec24533fdb433 ]

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 <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230829063457.54157-3-bgray@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/kernel/hw_breakpoint_constraints.c b/arch/powerpc/kernel/hw_breakpoint_constraints.c
index a74623025f3ab87b5a3375bab26e19c25b1ae173..9e51801c49152e32236b4ef5aa8a89ee05501445 100644 (file)
--- 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);