aad5f69bc1
There are three places where we access uninitialized memmaps, namely: - /proc/kpagecount - /proc/kpageflags - /proc/kpagecgroup We have initialized memmaps either when the section is online or when the page was initialized to the ZONE_DEVICE. Uninitialized memmaps contain garbage and in the worst case trigger kernel BUGs, especially with CONFIG_PAGE_POISONING. For example, not onlining a DIMM during boot and calling /proc/kpagecount with CONFIG_PAGE_POISONING: :/# cat /proc/kpagecount > tmp.test BUG: unable to handle page fault for address: fffffffffffffffe #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 114616067 P4D 114616067 PUD 114618067 PMD 0 Oops: 0000 [#1] SMP NOPTI CPU: 0 PID: 469 Comm: cat Not tainted 5.4.0-rc1-next-20191004+ #11 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 RIP: 0010:kpagecount_read+0xce/0x1e0 Code: e8 09 83 e0 3f 48 0f a3 02 73 2d 4c 89 e7 48 c1 e7 06 48 03 3d ab 51 01 01 74 1d 48 8b 57 08 480 RSP: 0018:ffffa14e409b7e78 EFLAGS: 00010202 RAX: fffffffffffffffe RBX: 0000000000020000 RCX: 0000000000000000 RDX: 0000000000000001 RSI: 00007f76b5595000 RDI: fffff35645000000 RBP: 00007f76b5595000 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000 R13: 0000000000020000 R14: 00007f76b5595000 R15: ffffa14e409b7f08 FS: 00007f76b577d580(0000) GS:ffff8f41bd400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: fffffffffffffffe CR3: 0000000078960000 CR4: 00000000000006f0 Call Trace: proc_reg_read+0x3c/0x60 vfs_read+0xc5/0x180 ksys_read+0x68/0xe0 do_syscall_64+0x5c/0xa0 entry_SYSCALL_64_after_hwframe+0x49/0xbe For now, let's drop support for ZONE_DEVICE from the three pseudo files in order to fix this. To distinguish offline memory (with garbage memmap) from ZONE_DEVICE memory with properly initialized memmaps, we would have to check get_dev_pagemap() and pfn_zone_device_reserved() right now. The usage of both (especially, special casing devmem) is frowned upon and needs to be reworked. The fundamental issue we have is: if (pfn_to_online_page(pfn)) { /* memmap initialized */ } else if (pfn_valid(pfn)) { /* * ??? * a) offline memory. memmap garbage. * b) devmem: memmap initialized to ZONE_DEVICE. * c) devmem: reserved for driver. memmap garbage. * (d) devmem: memmap currently initializing - garbage) */ } We'll leave the pfn_zone_device_reserved() check in stable_page_flags() in place as that function is also used from memory failure. We now no longer dump information about pages that are not in use anymore - offline. Link: http://lkml.kernel.org/r/20191009142435.3975-2-david@redhat.com Fixes: |
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.