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powerpc/watchpoints: Disable preemption in thread_change_pc()

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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 1e60f3564b ("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
This commit is contained in:
Benjamin Gray 2023-08-29 16:34:55 +10:00 committed by Michael Ellerman
parent 4ff3ba4db5
commit cc879ab3ce
1 changed files with 6 additions and 1 deletions
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7
arch/powerpc/kernel/hw_breakpoint.c
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@ -230,13 +230,15 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
struct arch_hw_breakpoint *info; struct arch_hw_breakpoint *info;
int i; int i;
preempt_disable();
for (i = 0; i < nr_wp_slots(); i++) { for (i = 0; i < nr_wp_slots(); i++) {
struct perf_event *bp = __this_cpu_read(bp_per_reg[i]); struct perf_event *bp = __this_cpu_read(bp_per_reg[i]);
if (unlikely(bp && counter_arch_bp(bp)->perf_single_step)) if (unlikely(bp && counter_arch_bp(bp)->perf_single_step))
goto reset; goto reset;
} }
return; goto out;
reset: reset:
regs_set_return_msr(regs, regs->msr & ~MSR_SE); regs_set_return_msr(regs, regs->msr & ~MSR_SE);
@ -245,6 +247,9 @@ reset:
__set_breakpoint(i, info); __set_breakpoint(i, info);
info->perf_single_step = false; info->perf_single_step = false;
} }
out:
preempt_enable();
} }
static bool is_larx_stcx_instr(int type) static bool is_larx_stcx_instr(int type)