linux-kernel - Re: [PATCH V2 7/9] x86/alternative: Batch of patch operations

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Date:   Tue, 18 Dec 2018 12:31:34 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Zhou Chengming <zhouchengming1@...wei.com>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Chris von Recklinghausen <crecklin@...hat.com>,
        Jason Baron <jbaron@...mai.com>, Scott Wood <swood@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V2 7/9] x86/alternative: Batch of patch operations

On Tue, 18 Dec 2018 17:46:36 +0100
Daniel Bristot de Oliveira <bristot@...hat.com> wrote:

> +void text_poke_bp_batch(struct text_to_poke *tp, unsigned int nr_entries)
> +{
> +	unsigned int i;
> +	unsigned char int3 = 0xcc;
> +	int patched_all_but_first = 0;
> +
> +	bp_int3_tpv = tp;
> +	bp_int3_tpv_nr = nr_entries;
> +	bp_patching_in_progress = true;
> +	/*
> +	 * Corresponding read barrier in int3 notifier for making sure the
> +	 * in_progress and handler are correctly ordered wrt. patching.
> +	 */
> +	smp_wmb();
> +
> +	for (i = 0; i < nr_entries; i++)
> +		text_poke_bp_set_handler(tp[i].addr, tp[i].handler, int3);
> +
> +	on_each_cpu(do_sync_core, NULL, 1);
> +
> +	for (i = 0; i < nr_entries; i++) {
> +		if (tp->len - sizeof(int3) > 0) {

Should this be:

		if (tp[i].len - sizeof(int3) > 0) {

?

-- Steve

> +			patch_all_but_first_byte(tp[i].addr, tp[i].opcode,
> +						 tp[i].len, int3);
> +			patched_all_but_first++;
> +		}
> +	}
> +
> +	if (patched_all_but_first) {
> +		/*
> +		 * According to Intel, this core syncing is very likely
> +		 * not necessary and we'd be safe even without it. But
> +		 * better safe than sorry (plus there's not only Intel).
> +		 */
> +		on_each_cpu(do_sync_core, NULL, 1);
> +	}
> +
> +	for (i = 0; i < nr_entries; i++)
> +		patch_first_byte(tp[i].addr, tp[i].opcode, 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_int3_tpv_nr = 0;
> +	bp_int3_tpv = NULL;
> +	bp_patching_in_progress = false;
> +}