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    SubjectRe: [PATCH V5 5/7] x86/alternative: Batch of patch operations
    On Mon, Apr 01, 2019 at 10:58:17AM +0200, Daniel Bristot de Oliveira wrote:
    > + ip = (void *) regs->ip - sizeof(unsigned char);

    That one confused me mightily. Does that want to be:

    ip = (void *)regs->ip - LEN_INT3;

    or something? Even just a naked 1 would've been less confusing.

    >
    > + /*
    > + * Skip the binary search if there is a single member in the vector.
    > + */
    > + if (unlikely(bp_patching.nr_entries == 1))
    > + goto single_poke;
    > +
    > + tp = bsearch(ip, bp_patching.vec, bp_patching.nr_entries,
    > + sizeof(struct text_patch_loc),
    > + patch_cmp);
    > + if (!tp)
    > + return 0;
    > +
    > + /* set up the specified breakpoint detour */
    > + regs->ip = (unsigned long) tp->detour;
    > return 1;
    > +single_poke:
    > + if (ip == bp_patching.vec->addr) {
    > + regs->ip = (unsigned long) bp_patching.vec->detour;
    > + return 1;
    > + }
    > +
    > + return 0;

    if (bp_patching.nr_entries > 1) {
    tp = bsearch(ip, bp_patching.vec, bp_patching.nr_entries,
    sizeof(struct text_patch_loc), patch_cmp);
    if (!tp)
    return 0;
    } else {
    tp = bp_patching.vec;
    if (tp->addr != ip)
    return 0;
    }

    regs->ip = (unsigned long)tp->detour;
    return 1;
    > }
    > NOKPROBE_SYMBOL(poke_int3_handler);

    > +void text_poke_bp_batch(struct text_patch_loc *tp, unsigned int nr_entries)
    > {
    > + int patched_all_but_first = 0;
    > unsigned char int3 = 0xcc;
    > + unsigned int i;
    >
    > lockdep_assert_held(&text_mutex);
    >
    > + bp_patching.vec = tp;
    > + bp_patching.nr_entries = 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();
    >
    > + /*
    > + * First step: add a int3 trap to the address that will be patched.
    > + */
    > + for (i = 0; i < nr_entries; i++)
    > + text_poke(tp[i].addr, &int3, sizeof(int3));
    >
    > on_each_cpu(do_sync_core, NULL, 1);
    >
    > + /*
    > + * Second step: update all but the first byte of the patched range.
    > + */
    > + for (i = 0; i < nr_entries; i++) {
    > + if (tp[i].len - sizeof(int3) > 0) {
    > + text_poke((char *)tp[i].addr + sizeof(int3),
    > + (const char *)tp[i].opcode + sizeof(int3),
    > + tp[i].len - sizeof(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
    > @@ -821,15 +874,52 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
    > on_each_cpu(do_sync_core, NULL, 1);
    > }
    >
    > + /*
    > + * Third step: replace the first byte (int3) by the first byte of
    > + * replacing opcode.
    > + */
    > + for (i = 0; i < nr_entries; i++)
    > + text_poke(tp[i].addr, tp[i].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.vec = NULL;
    > + bp_patching.nr_entries = 0;
    > + bp_patching.in_progress = false;
    > +}

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