On Mon, Oct 05, 2020 at 02:41:53AM +0300, Jarkko Sakkinen wrote: > On Sun, Oct 04, 2020 at 11:27:50PM +0100, Matthew Wilcox wrote: > > int ret = 0; > > > > mutex_lock(&encl->lock); > > rcu_read_lock(); > > Right, so xa_*() take RCU lock implicitly and xas_* do not. Not necessarily the RCU lock ... I did document all this in xarray.rst: https://www.kernel.org/doc/html/latest/core-api/xarray.html > > while (xas.index < idx_end) { > > page = xas_next(&xas); > > It should iterate through every possible page index within the range, > even the ones that do not have an entry, i.e. this loop also checks > that there are no empty slots. > > Does xas_next() go through every possible index, or skip the non-empty > ones? xas_next(), as its documentation says, will move to the next array index: https://www.kernel.org/doc/html/latest/core-api/xarray.html#c.xas_next > > if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) > > ret = -EACCESS; > > break; > > } > > } > > rcu_read_unlock(); > > mutex_unlock(&encl->lock); > > In my Geminilake NUC the maximum size of the address space is 64GB for > an enclave, and it is not fixed but can grow in microarchitectures > beyond that. > > That means that in (*artificial*) worst case the locks would be kept for > 64*1024*1024*1024/4096 = 16777216 iterations. Oh, there's support for that on the XArray API too. xas_lock_irq(&xas); xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) { xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE); if (++tagged % XA_CHECK_SCHED) continue; xas_pause(&xas); xas_unlock_irq(&xas); cond_resched(); xas_lock_irq(&xas); } xas_unlock_irq(&xas);
