From 8c2500228b8f5ea9abcc4522dedca0963edd2f3b Mon Sep 17 00:00:00 2001 From: Benjamin Gray Date: Tue, 29 Aug 2023 16:34:55 +1000 Subject: [PATCH] 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 Signed-off-by: Michael Ellerman Link: https://msgid.link/20230829063457.54157-2-bgray@linux.ibm.com Signed-off-by: Sasha Levin --- arch/powerpc/kernel/hw_breakpoint.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c index f4e8f21046f5..6e5bed50c357 100644 --- a/arch/powerpc/kernel/hw_breakpoint.c +++ b/arch/powerpc/kernel/hw_breakpoint.c @@ -479,11 +479,13 @@ 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->msr &= ~MSR_SE; @@ -492,6 +494,9 @@ reset: __set_breakpoint(i, info); tsk->thread.last_hit_ubp[i] = NULL; } + +out: + preempt_enable(); } static bool is_larx_stcx_instr(int type)