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Petr Vaněk efb5973459 mm: fix folio_pte_batch() on XEN PV 
commit 7b08b74f3d upstream.

On XEN PV, folio_pte_batch() can incorrectly batch beyond the end of a
folio due to a corner case in pte_advance_pfn().  Specifically, when the
PFN following the folio maps to an invalidated MFN,

	expected_pte = pte_advance_pfn(expected_pte, nr);

produces a pte_none().  If the actual next PTE in memory is also
pte_none(), the pte_same() succeeds,

	if (!pte_same(pte, expected_pte))
		break;

the loop is not broken, and batching continues into unrelated memory.

For example, with a 4-page folio, the PTE layout might look like this:

[   53.465673] [ T2552] folio_pte_batch: printing PTE values at addr=0x7f1ac9dc5000
[   53.465674] [ T2552]   PTE[453] = 000000010085c125
[   53.465679] [ T2552]   PTE[454] = 000000010085d125
[   53.465682] [ T2552]   PTE[455] = 000000010085e125
[   53.465684] [ T2552]   PTE[456] = 000000010085f125
[   53.465686] [ T2552]   PTE[457] = 0000000000000000 <-- not present
[   53.465689] [ T2552]   PTE[458] = 0000000101da7125

pte_advance_pfn(PTE[456]) returns a pte_none() due to invalid PFN->MFN
mapping.  The next actual PTE (PTE[457]) is also pte_none(), so the loop
continues and includes PTE[457] in the batch, resulting in 5 batched
entries for a 4-page folio.  This triggers the following warning:

[   53.465751] [ T2552] page: refcount:85 mapcount:20 mapping:ffff88813ff4f6a8 index:0x110 pfn:0x10085c
[   53.465754] [ T2552] head: order:2 mapcount:80 entire_mapcount:0 nr_pages_mapped:4 pincount:0
[   53.465756] [ T2552] memcg:ffff888003573000
[   53.465758] [ T2552] aops:0xffffffff8226fd20 ino:82467c dentry name(?):"libc.so.6"
[   53.465761] [ T2552] flags: 0x2000000000416c(referenced|uptodate|lru|active|private|head|node=0|zone=2)
[   53.465764] [ T2552] raw: 002000000000416c ffffea0004021f08 ffffea0004021908 ffff88813ff4f6a8
[   53.465767] [ T2552] raw: 0000000000000110 ffff888133d8bd40 0000005500000013 ffff888003573000
[   53.465768] [ T2552] head: 002000000000416c ffffea0004021f08 ffffea0004021908 ffff88813ff4f6a8
[   53.465770] [ T2552] head: 0000000000000110 ffff888133d8bd40 0000005500000013 ffff888003573000
[   53.465772] [ T2552] head: 0020000000000202 ffffea0004021701 000000040000004f 00000000ffffffff
[   53.465774] [ T2552] head: 0000000300000003 8000000300000002 0000000000000013 0000000000000004
[   53.465775] [ T2552] page dumped because: VM_WARN_ON_FOLIO((_Generic((page + nr_pages - 1), const struct page *: (const struct folio *)_compound_head(page + nr_pages - 1), struct page *: (struct folio *)_compound_head(page + nr_pages - 1))) != folio)

Original code works as expected everywhere, except on XEN PV, where
pte_advance_pfn() can yield a pte_none() after balloon inflation due to
MFNs invalidation.  In XEN, pte_advance_pfn() ends up calling
__pte()->xen_make_pte()->pte_pfn_to_mfn(), which returns pte_none() when
mfn == INVALID_P2M_ENTRY.

The pte_pfn_to_mfn() documents that nastiness:

	If there's no mfn for the pfn, then just create an
	empty non-present pte.  Unfortunately this loses
	information about the original pfn, so
	pte_mfn_to_pfn is asymmetric.

While such hacks should certainly be removed, we can do better in
folio_pte_batch() and simply check ahead of time how many PTEs we can
possibly batch in our folio.

This way, we can not only fix the issue but cleanup the code: removing the
pte_pfn() check inside the loop body and avoiding end_ptr comparison +
arithmetic.

Link: https://lkml.kernel.org/r/20250502215019.822-2-arkamar@atlas.cz
Fixes: f8d937761d ("mm/memory: optimize fork() with PTE-mapped THP")
Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Petr Vaněk <arkamar@atlas.cz>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-05-18 08:24:51 +02:00
arch x86/mm: Eliminate window where TLB flushes may be inadvertently skipped 2025-05-18 08:24:51 +02:00
block blk-mq: create correct map for fallback case 2025-05-09 09:50:48 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: Kconfig - Select LIB generic option 2025-05-02 07:59:33 +02:00
Documentation bpf: Add namespace to BPF internal symbols 2025-05-02 07:59:04 +02:00
drivers staging: axis-fifo: Correct handling of tx_fifo_depth for size validation 2025-05-18 08:24:51 +02:00
fs erofs: ensure the extra temporary copy is valid for shortened bvecs 2025-05-18 08:24:48 +02:00
include net: export a helper for adding up queue stats 2025-05-18 08:24:50 +02:00
init rust: clean Rust 1.88.0's unnecessary_transmutes lint 2025-05-18 08:24:51 +02:00
io_uring io_uring: always do atomic put from iowq 2025-05-02 07:59:21 +02:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel kernel: globalize lookup_or_create_module_kobject() 2025-05-09 09:50:52 +02:00
lib crypto: lib/Kconfig - Hide arch options from user 2025-05-02 07:59:32 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: fix folio_pte_batch() on XEN PV 2025-05-18 08:24:51 +02:00
net net: export a helper for adding up queue stats 2025-05-18 08:24:50 +02:00
rust rust: clean Rust 1.88.0's unnecessary_transmutes lint 2025-05-18 08:24:51 +02:00
samples tracing: Verify event formats that have "%*p.." 2025-05-02 07:58:52 +02:00
scripts objtool: Silence more KCOV warnings, part 2 2025-05-02 07:59:33 +02:00
security landlock: Prepare to add second errata 2025-04-20 10:15:56 +02:00
sound ASoC: simple-card-utils: Fix pointer check in graph_util_parse_link_direction 2025-05-09 09:50:46 +02:00
tools objtool/rust: add one more noreturn Rust function for Rust 1.87.0 2025-05-18 08:24:51 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow building irqbypass.ko as as module when kvm.ko is a module 2025-04-20 10:15:54 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-18 08:24:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add entry for the Rust alloc module 2025-03-13 13:01:47 +01:00
Makefile Linux 6.12.28 2025-05-09 09:50:53 +02:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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 reStructuredText 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.