On Fri, Jun 26, 2015 at 08:02:03PM -0700, Mark Hairgrove wrote: > On Fri, 26 Jun 2015, Jerome Glisse wrote: > > On Thu, Jun 25, 2015 at 04:05:48PM -0700, Mark Hairgrove wrote: > > > On Thu, 21 May 2015, [email protected] wrote: > > > > From: Jérôme Glisse <[email protected]> > > > > [...] > > > > > > > > + /* update() - update device mmu following an event. > > > > + * > > > > + * @mirror: The mirror that link process address space with the > > > > device. > > > > + * @event: The event that triggered the update. > > > > + * Returns: 0 on success or error code {-EIO, -ENOMEM}. > > > > + * > > > > + * Called to update device page table for a range of address. > > > > + * The event type provide the nature of the update : > > > > + * - Range is no longer valid (munmap). > > > > + * - Range protection changes (mprotect, COW, ...). > > > > + * - Range is unmapped (swap, reclaim, page migration, ...). > > > > + * - Device page fault. > > > > + * - ... > > > > + * > > > > + * Thought most device driver only need to use pte_mask as it > > > > reflects > > > > + * change that will happen to the HMM page table ie : > > > > + * new_pte = old_pte & event->pte_mask; > > > > > > Documentation request: It would be useful to break down exactly what is > > > required from the driver for each event type here, and what extra > > > information is provided by the type that isn't provided by the pte_mask. > > > > Mostly event tell you if you need to free or not the device page table for > > the range, which is not something you can infer from the pte_mask reliably. > > Difference btw migration and munmap for instance, same pte_mask but range > > is still valid in the migration case it will just be backed by a new set of > > pages. > > Given that event->pte_mask and event->type provide redundant information, > are they both necessary?
Like said, you can not infer event->type from pte_mask but you can infer pte_mask from event->type. The idea is behind providing pte_mask is that simple driver can just use that with the iter walk and simply mask the HMM page table entry they read ((*ptep) & pte_mask) to repopulate the device page table. So yes pte_mask is redundant but i think it will be useful for a range of device driver. Cheers, Jérôme -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
