When the kallsyms relative base was introduced, per-CPU variable
references on x86_64 SMP were implemented as offsets into the respective
per-CPU region, rather than offsets relative to the location of the
variable's template in the kernel image, which is how other
architectures implement it.
This required kallsyms to reason about the difference between the two,
and the sign of the value in the kallsyms_offsets[] array was used to
distinguish them. This meant that negative offsets were not permitted
for ordinary variables, and so it was crucial that the relative base was
chosen such that all offsets were positive numbers.
This is no longer needed: instead, the offsets can simply be encoded as
values in the range -/+ 2 GiB, which is precisely what PC32 relocations
provide on most architectures. So it is possible to simplify the logic,
and just use _text as the anchor directly, and let the linker calculate
the final value based on the location of the entry itself.
Some architectures (nios2, extensa) do not support place-relative
relocations at all, but these are all 32-bit and non-relocatable, and so
there is no need for place-relative relocations in the first place, and
the actual symbol values can just be stored directly.
This makes all entries in the kallsyms_offsets[] array visible as
place-relative references in the ELF metadata, which will be important
when implementing ELF-based fg-kaslr.
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://patch.msgid.link/20260116093359.2442297-6-ardb+git@google.com
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Introduce a generic infrastructure for tracking recoverable hardware
errors (HW errors that are visible to the OS but does not cause a panic)
and record them for vmcore consumption. This aids post-mortem crash
analysis tools by preserving a count and timestamp for the last occurrence
of such errors. On the other side, correctable errors, which the OS
typically remains unaware of because the underlying hardware handles them
transparently, are less relevant for crash dump and therefore are NOT
tracked in this infrastructure.
Add centralized logging for sources of recoverable hardware errors based
on the subsystem it has been notified.
hwerror_data is write-only at kernel runtime, and it is meant to be read
from vmcore using tools like crash/drgn. For example, this is how it
looks like when opening the crashdump from drgn.
>>> prog['hwerror_data']
(struct hwerror_info[1]){
{
.count = (int)844,
.timestamp = (time64_t)1752852018,
},
...
This helps fleet operators quickly triage whether a crash may be
influenced by hardware recoverable errors (which executes a uncommon code
path in the kernel), especially when recoverable errors occurred shortly
before a panic, such as the bug fixed by commit ee62ce7a1d ("page_pool:
Track DMA-mapped pages and unmap them when destroying the pool")
This is not intended to replace full hardware diagnostics but provides a
fast way to correlate hardware events with kernel panics quickly.
Rare machine check exceptions—like those indicated by mce_flags.p5 or
mce_flags.winchip—are not accounted for in this method, as they fall
outside the intended usage scope for this feature's user base.
[leitao@debian.org: add hw-recoverable-errors to toctree]
Link: https://lkml.kernel.org/r/20251127-vmcoreinfo_fix-v1-1-26f5b1c43da9@debian.org
Link: https://lkml.kernel.org/r/20251010-vmcore_hw_error-v5-1-636ede3efe44@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Suggested-by: Tony Luck <tony.luck@intel.com>
Suggested-by: Shuai Xue <xueshuai@linux.alibaba.com>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com> [APEI]
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Bob Moore <robert.moore@intel.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Konrad Rzessutek Wilk <konrad.wilk@oracle.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: "Oliver O'Halloran" <oohall@gmail.com>
Cc: Omar Sandoval <osandov@osandov.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
By using a few values in the top byte, users of page_type can store up to
24 bits of additional data in page_type. It also reduces the code size as
(with replacement of READ_ONCE() with data_race()), the kernel can check
just a single byte. eg:
ffffffff811e3a79: 8b 47 30 mov 0x30(%rdi),%eax
ffffffff811e3a7c: 55 push %rbp
ffffffff811e3a7d: 48 89 e5 mov %rsp,%rbp
ffffffff811e3a80: 25 00 00 00 82 and $0x82000000,%eax
ffffffff811e3a85: 3d 00 00 00 80 cmp $0x80000000,%eax
ffffffff811e3a8a: 74 4d je ffffffff811e3ad9 <folio_mapping+0x69>
becomes:
ffffffff811e3a69: 80 7f 33 f5 cmpb $0xf5,0x33(%rdi)
ffffffff811e3a6d: 55 push %rbp
ffffffff811e3a6e: 48 89 e5 mov %rsp,%rbp
ffffffff811e3a71: 74 4d je ffffffff811e3ac0 <folio_mapping+0x60>
replacing three instructions with one.
[wangkefeng.wang@huawei.com: fix ubsan warnings]
Link: https://lkml.kernel.org/r/2d19c48a-c550-4345-bf36-d05cd303c5de@huawei.com
Link: https://lkml.kernel.org/r/20240821173914.2270383-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The current folio_test_hugetlb() can be fooled by a concurrent folio split
into returning true for a folio which has never belonged to hugetlbfs.
This can't happen if the caller holds a refcount on it, but we have a few
places (memory-failure, compaction, procfs) which do not and should not
take a speculative reference.
Since hugetlb pages do not use individual page mapcounts (they are always
fully mapped and use the entire_mapcount field to record the number of
mappings), the PageType field is available now that page_mapcount()
ignores the value in this field.
In compaction and with CONFIG_DEBUG_VM enabled, the current implementation
can result in an oops, as reported by Luis. This happens since 9c5ccf2db0
("mm: remove HUGETLB_PAGE_DTOR") effectively added some VM_BUG_ON() checks
in the PageHuge() testing path.
[willy@infradead.org: update vmcoreinfo]
Link: https://lkml.kernel.org/r/ZgGZUvsdhaT1Va-T@casper.infradead.org
Link: https://lkml.kernel.org/r/20240321142448.1645400-6-willy@infradead.org
Fixes: 9c5ccf2db0 ("mm: remove HUGETLB_PAGE_DTOR")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Luis Chamberlain <mcgrof@kernel.org>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218227
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
