powerpc/watchpoints: Disable preemption in thread_change_pc()

[ Upstream commit cc879ab3ce39bc39f9b1d238b283f43a5f6f957d ]

thread_change_pc() uses CPU local data, so must be protected from
swapping CPUs while it is reading the breakpoint struct.

The error is more noticeable after 1e60f3564bad ("powerpc/watchpoints:
Track perf single step directly on the breakpoint"), which added an
unconditional __this_cpu_read() call in thread_change_pc(). However the
existing __this_cpu_read() that runs if a breakpoint does need to be
re-inserted has the same issue.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230829063457.54157-2-bgray@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 8db1a15d7acbe17815f2a843242b5ea5339fbcf1..a72f86c130488de153780c65865651b4430e7314 100644 (file)
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -505,11 +505,13 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
        struct arch_hw_breakpoint *info;
        int i;
 
+       preempt_disable();
+
        for (i = 0; i < nr_wp_slots(); i++) {
                if (unlikely(tsk->thread.last_hit_ubp[i]))
                        goto reset;
        }
-       return;
+       goto out;
 
 reset:
        regs_set_return_msr(regs, regs->msr & ~MSR_SE);
@@ -518,6 +520,9 @@ reset:
                __set_breakpoint(i, info);
                tsk->thread.last_hit_ubp[i] = NULL;
        }
+
+out:
+       preempt_enable();
 }
 
 static bool is_larx_stcx_instr(int type)