On 11/1/21 01:06, John David Anglin wrote: > On 2021-10-31 8:01 p.m., John David Anglin wrote: >> On 2021-10-31 7:56 p.m., John David Anglin wrote: >>> n 2021-10-31 7:07 p.m., Helge Deller wrote: >>>> On 10/31/21 23:47, John David Anglin wrote: >>>>> My sense is the invalidate patch isn't correct. The main difference between pdc and fdc is that >>>>> it is optional whether pdc writes the cache line back to memory when it's dirty at priority 0. >>>> That's true, nevertheless I've seen different behaviour on real hardware. >>>> >>>> It might be, that: >>>> >>>> - flush_kernel_vmap_range((void *)fixmap, (p-fixmap) * sizeof(*p)); >>>> + invalidate_kernel_vmap_range((void *)fixmap, (p-fixmap) * sizeof(*p)); >>>> (here the flush might be sufficient) >>>> if (mapped) >>>> patch_unmap(FIX_TEXT_POKE0, &flags); >>>> + invalidate_kernel_vmap_range((void *)start, end - start); >>>> (but here the pdc is necessary to actually drop data from I-cache) >>>> flush_icache_range(start, end); >>>> >>>> I can test tomorrow... >>> Maybe sync is needed before releasing lock. pdc/fdc are weakly ordered. >> Forget that. There already is a sync. > Could it be we incorrectly change the flush/purge operations to nops? > 89: ALTERNATIVE(88b, 89b, ALT_COND_NO_DCACHE, INSN_NOP) No, can't be. The alternative patching hasn't run yet when the kprobe testcases run. Nevertheless, I don't fully understand it yet. The same code works differently depending on the machine. Helge
