On Wed, 2013-07-10 at 23:31 +0200, Jiri Kosina wrote:
> Introduce a method for run-time instrucntion patching on a live SMP kernel
> based on int3 breakpoint, completely avoiding the need for stop_machine().
Yet more trivia:
instruction typo
> The way this is achieved:
>
> - add a int3 trap to the address that will be patched
> - sync cores
> - update all but the first byte of the patched range
> - sync cores
> - replalace the first byte (int3) by the first byte of
replace typo
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
[]
> +static int int3_notify(struct notifier_block *self, unsigned long val, void
> *data)
> +{
> + struct die_args *args = data;
> + struct pt_regs *regs = args->regs;
> +
> + /* bp_patching_in_progress */
> + smp_rmb();
> +
> + if (likely(!bp_patching_in_progress))
> + return NOTIFY_DONE;
> +
> + /* we are not interested in non-int3 faults and ring > 0 faults */
> + if (val != DIE_INT3 || !regs || user_mode_vm(regs)
> + || (unsigned long) bp_int3_addr != regs->ip)
> + return NOTIFY_DONE;
> +
> + /* set up the specified breakpoint handler */
> + args->regs->ip = (unsigned long) bp_int3_handler;
Probably better to use regs->ip as that's what's used
in the test above.
I'd also change the test to order the regs->ip first
if (val != DIE_INT3 || !regs || user_mode_vm(regs) ||
regs->ip != (unsigned long) bp_int3_addr)
return NOTIFY_DONE;
regs->ip = (unsigned long) bp_int3_handler;
> +/*
> + * text_poke_bp() -- update instructions on live kernel on SMP
> + * @addr: address to patch
> + * @opcode: opcode of new instruction
> + * @len: length to copy
> + * @handler: address to jump to when the temporary breakpoint is hit
> + *
kernel-doc?
> +
> + * Modify multi-byte instruction by using int3 breakpoint on SMP.
> + * In contrary to text_poke_smp(), we completely avoid stop_machine() here,
> + * and achieve the synchronization using int3 breakpoint.
> + *
> + * The way it is done:
> + * - add a int3 trap to the address that will be patched
> + * - sync cores
> + * - update all but the first byte of the patched range
> + * - sync cores
> + * - replalace the first byte (int3) by the first byte of
same typo
> + /*
> + * corresponding read barrier in int3 notifier for
> + * making sure the in_progress flags is correctly ordered wrt.
> + * patching */
Some might care about the comment style.
/*
* foo
*/
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