Peter Xu <peterx@xxxxxxxxxx> writes: > We've got a bunch of special swap entries that stores PFN inside the swap > offset fields. To fetch the PFN, normally the user just calls swp_offset() > assuming that'll be the PFN. > > Add a helper swp_offset_pfn() to fetch the PFN instead, fetching only the > max possible length of a PFN on the host, meanwhile doing proper check with > MAX_PHYSMEM_BITS to make sure the swap offsets can actually store the PFNs > properly always using the BUILD_BUG_ON() in is_pfn_swap_entry(). > > One reason to do so is we never tried to sanitize whether swap offset can > really fit for storing PFN. At the meantime, this patch also prepares us > with the future possibility to store more information inside the swp offset > field, so assuming "swp_offset(entry)" to be the PFN will not stand any > more very soon. > > Replace many of the swp_offset() callers to use swp_offset_pfn() where > proper. Note that many of the existing users are not candidates for the > replacement, e.g.: > > (1) When the swap entry is not a pfn swap entry at all, or, > (2) when we wanna keep the whole swp_offset but only change the swp type. > > For the latter, it can happen when fork() triggered on a write-migration > swap entry pte, we may want to only change the migration type from > write->read but keep the rest, so it's not "fetching PFN" but "changing > swap type only". They're left aside so that when there're more information > within the swp offset they'll be carried over naturally in those cases. > > Since at it, dropping hwpoison_entry_to_pfn() because that's exactly what > the new swp_offset_pfn() is about. > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> The patch itself looks good. But I searched swp_entry() in kernel source code, and found that we need to do more. For example, in pte_to_pagemap_entry() frame = swp_type(entry) | (swp_offset(entry) << MAX_SWAPFILES_SHIFT); If it's a migration entry, we need frame = swp_type(entry) | (swp_offset_pfn(entry) << MAX_SWAPFILES_SHIFT); So I think you need to search all swp_offset() calling in the kernel source and check whether they need to be changed. Best Regards, Huang, Ying [snip]
