On Tue, Aug 23, 2022 at 03:01:09PM -0600, Yu Zhao wrote: > On Thu, Aug 11, 2022 at 8:33 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote: > > > > 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> > > > > LGTM, Thanks! > > > > Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> > > Hi, > > I hit the following crash on mm-everything-2022-08-22-22-59. Please take a look. > > Thanks. > > kernel BUG at include/linux/swapops.h:117! > CPU: 46 PID: 5245 Comm: EventManager_De Tainted: G S O L > 6.0.0-dbg-DEV #2 > RIP: 0010:pfn_swap_entry_to_page+0x72/0xf0 > Code: c6 48 8b 36 48 83 fe ff 74 53 48 01 d1 48 83 c1 08 48 8b 09 f6 > c1 01 75 7b 66 90 48 89 c1 48 8b 09 f6 c1 01 74 74 5d c3 eb 9e <0f> 0b > 48 ba ff ff ff ff 03 00 00 00 eb ae a9 ff 0f 00 00 75 13 48 > RSP: 0018:ffffa59e73fabb80 EFLAGS: 00010282 > RAX: 00000000ffffffe8 RBX: 0c00000000000000 RCX: ffffcd5440000000 > RDX: 1ffffffffff7a80a RSI: 0000000000000000 RDI: 0c0000000000042b > RBP: ffffa59e73fabb80 R08: ffff9965ca6e8bb8 R09: 0000000000000000 > R10: ffffffffa5a2f62d R11: 0000030b372e9fff R12: ffff997b79db5738 > R13: 000000000000042b R14: 0c0000000000042b R15: 1ffffffffff7a80a > FS: 00007f549d1bb700(0000) GS:ffff99d3cf680000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000440d035b3180 CR3: 0000002243176004 CR4: 00000000003706e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > change_pte_range+0x36e/0x880 > change_p4d_range+0x2e8/0x670 > change_protection_range+0x14e/0x2c0 > mprotect_fixup+0x1ee/0x330 > do_mprotect_pkey+0x34c/0x440 > __x64_sys_mprotect+0x1d/0x30 The VM_BUG_ON added in this patch seems to have revealed a real bug, because we probably shouldn't call pfn_swap_entry_to_page() upon e.g. a genuine swap pte. I'll post a patch shortly, thanks. -- Peter Xu
