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x86: Clarify/fix no-op barriers for text_poke_bp()

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So I was looking at text_poke_bp() today and I couldn't make sense of
the barriers there.

How's for something like so?

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: masami.hiramatsu.pt@hitachi.com
Link: http://lkml.kernel.org/r/20170731102154.f57cvkjtnbmtctk6@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2017-07-31 12:21:54 +02:00 committed by Ingo Molnar
parent e137a4d8f4
commit 01651324ed
1 changed files with 16 additions and 6 deletions
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22
arch/x86/kernel/alternative.c
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@ -742,7 +742,16 @@ static void *bp_int3_handler, *bp_int3_addr;
int poke_int3_handler(struct pt_regs *regs)
{
/* bp_patching_in_progress */
/*
* Having observed our INT3 instruction, we now must observe
* bp_patching_in_progress.
*
* in_progress = TRUE INT3
* WMB RMB
* write INT3 if (in_progress)
*
* Idem for bp_int3_handler.
*/
smp_rmb();
if (likely(!bp_patching_in_progress))
@ -788,9 +797,8 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
bp_int3_addr = (u8 *)addr + sizeof(int3);
bp_patching_in_progress = true;
/*
* Corresponding read barrier in int3 notifier for
* making sure the in_progress flags is correctly ordered wrt.
* patching
* Corresponding read barrier in int3 notifier for making sure the
* in_progress and handler are correctly ordered wrt. patching.
*/
smp_wmb();
@ -815,9 +823,11 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
text_poke(addr, opcode, sizeof(int3));
on_each_cpu(do_sync_core, NULL, 1);
/*
* sync_core() implies an smp_mb() and orders this store against
* the writing of the new instruction.
*/
bp_patching_in_progress = false;
smp_wmb();
return addr;
}