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Like other architectures such as x86, arm64, riscv, powerpc and s390,
select THREAD_INFO_IN_TASK for LoongArch to move thread_info off the
stack into task_struct. This follows modern kernel standards and also
makes the system more secure.
With this patch, thread_info is included in task_struct at an offset
of 0 instead of being placed at the bottom of the kernel stack. Thus,
the $tp register points to both thread_info and task_struct.
To support this, introduce a per-CPU variable cpu_tasks to store the
pointer to the current task_struct. This decouples the recovery of the
$tp register from the stack pointer during exception entry.
Then initialize cpu_tasks for the primary and secondary CPUs during
arch-specific setup and SMP boot paths. To eliminate the dangerous
windows during the early initialization where the cpu_tasks remains
uninitialized, set_current() is invoked as early as possible in both
setup_arch() and start_secondary(). This ensures the $tp recovery
barrier is armed in case any early boot exceptions or kernel panics
occur.
Modify SAVE_SOME and handle_syscall to restore the $tp register from
cpu_tasks, and also use the la_abs absolute addressing for cpu_tasks
access in assembly to bypass the relocation limits within exception
handling sections. By advancing the preservation of u0 in SAVE_SOME,
we reuse the PERCPU_BASE_KS value in u0 for the cpu_tasks calculation,
effectively eliminating a duplicate csrrd instruction execution on SMP
platforms.
Update <asm/switch_to.h> and <kernel/switch.S> to fully support the
CONFIG_THREAD_INFO_IN_TASK feature.
Remove the obsolete next_ti argument from __switch_to(), which shifts
the remaining arguments ahead in the calling convention (sched_ra from
a3 to a2, and sched_cfa from a4 to a3). Under the new configuration,
__switch_to() now directly derives the thread pointer ($tp) from the
next task_struct pointer in a1.
To preserve the optimal and clean "move tp, a1" path for 64-bit kernels,
the thread pointer ($tp) is assigned directly from a1 in the core path.
For 32-bit kernels, where a1 carries a 2000-byte structural pointer bias
at entry, an explicit adjustment "PTR_ADDI tp, tp, -TASK_STRUCT_OFFSET"
is introduced at the function exit.
In the context of __switch_to(), local interrupts are disabled, and the
kernel is in a critical switching phase where handling any synchronous
exception is practically impossible and prohibited.
If any synchronous exception or watchpoint does trigger in this narrow
window, it constitutes a fatal double fault and the kernel is expected
to die/panic immediately anyway. Therefore, the temporary biased value
in $tp is safe and acceptable here.
Additionally, evaluate the stack lookup as a single load instruction
"LONG_LPTR t0, a1, (TASK_STACK - TASK_STRUCT_OFFSET)", this perfectly
satisfies both 32-bit and 64-bit kernels. Using the "next" pointer in
a1 as the base register, rather than $tp, effectively unchains the data
dependency (RAW hazard) from the preceding move instruction, maximizing
the instruction-level parallelism and superscalar execution efficiency
while naturally adapting the structural shift.
With CONFIG_THREAD_INFO_IN_TASK enabled, the kernel stack life cycle is
decoupled from task_struct and can be freed concurrently.
Currently, show_stacktrace() reads raw stack data via __get_addr() and
subsequently calls show_backtrace() to unwind the frame, without holding
any reference to the target task's stack. If show_stacktrace() is called
on a concurrently exiting task, it could attempt to read from a freed or
reallocated kernel stack. This introduces a severe use-after-free (UAF)
read risk or kernel panics.
Wrap the entire stack inspection process inside show_stacktrace() with
a try_get_task_stack() and put_task_stack() pair. This ensures the task
stack remains pinned safely during both the raw stack data dump loop and
the subsequent stack unwinding phase.
Also, ensure that the task pointer is initialized to "current" early if
it is NULL, so that try_get_task_stack() always operates on a valid task
reference.
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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It seems that ./Documentation/features/scripts/features-refresh.sh was most
recently used in December 2022, with the latest kernel release v6.1-rc7 at
that time (see commit 7f2e60ff51ca ("Documentation/features: Update feature
lists for 6.1") to update the feature lists in this subdirectory. All
further changes to Documentation/features/ since then have probably been
done manually, without checking for changes in other architectures and
features, that missed to update this part of the documentation.
Running ./Documentation/features/scripts/features-refresh.sh now showed
seven changes of supported features in various architectures (one in arc,
two in parisc, one in riscv, one in openrisc, and two in um), which were
not reflected yet in the current documentation.
To confirm the sanity of this script's suggested changes, I checked if the
commit messages confirm that the features have in fact been added in the
following commits:
- commit f122668ddcce ("ARC: Add eBPF JIT support")
- commit 4800a6215e33 ("parisc: Wire up eBPF JIT compiler")
- commit a869b8c29f86 ("riscv: enable mseal sysmap for RV64")
- commit 2f681ba4b352 ("um: move thread info into task")
- commit 3f17fed21491 ("um: switch to regset API and depend on XSTATE")
- commit 7ce8716e2769 ("openrisc: Add HAVE_REGS_AND_STACK_ACCESS_API support")
- commit b5ff52be8913 ("parisc: Convert to generic clockevents")
So, update all documents to the current state with features-refresh.sh.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20250925073634.112142-1-lukas.bulwahn@redhat.com>
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Itanium (IA64) is going away, so drop it from the kernel feature
documentation.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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Fix typos in Documentation.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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The official arch name is LoongArch [1], we should use small letter
loongarch instead of loong in Documentation/features, just use the
features-refresh.sh to refresh all the related files.
[1] https://www.kernel.org/doc/html/latest/loongarch/index.html
Fixes: 5860800e8696 ("Documentation/features: Update the arch support status files")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/1670156327-9631-3-git-send-email-yangtiezhu@loongson.cn
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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The arch support status files don't match reality as of v5.19-rc1,
use the features-refresh.sh to refresh all the arch-support.txt files
in place. The main effect is to add entries for the new loong
architecture.
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Link: https://lore.kernel.org/r/20220609025656.143460-1-zhengzengkai@huawei.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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asm-generic
* 'remove-h8300' of git://git.infradead.org/users/hch/misc:
remove the h8300 architecture
This is clearly the least actively maintained architecture we have at
the moment, and probably the least useful. It is now the only one that
does not support MMUs at all, and most of the boards only support 4MB
of RAM, out of which the defconfig kernel needs more than half just
for .text/.data.
Guenter Roeck did the original patch to remove the architecture in 2013
after it had already been obsolete for a while, and Yoshinori Sato brought
it back in a much more modern form in 2015. Looking at the git history
since the reinstantiation, it's clear that almost all commits in the tree
are build fixes or cross-architecture cleanups:
$ git log --no-merges --format=%an v4.5.. arch/h8300/ | sort | uniq
-c | sort -rn | head -n 12
25 Masahiro Yamada
18 Christoph Hellwig
14 Mike Rapoport
9 Arnd Bergmann
8 Mark Rutland
7 Peter Zijlstra
6 Kees Cook
6 Ingo Molnar
6 Al Viro
5 Randy Dunlap
4 Yury Norov
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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The nds32 architecture, also known as AndeStar V3, is a custom 32-bit
RISC target designed by Andes Technologies. Support was added to the
kernel in 2016 as the replacement RISC-V based V5 processors were
already announced, and maintained by (current or former) Andes
employees.
As explained by Alan Kao, new customers are now all using RISC-V,
and all known nds32 users are already on longterm stable kernels
provided by Andes, with no development work going into mainline
support any more.
While the port is still in a reasonably good shape, it only gets
worse over time without active maintainers, so it seems best
to remove it before it becomes unusable. As always, if it turns
out that there are mainline users after all, and they volunteer
to maintain the port in the future, the removal can be reverted.
Link: https://lore.kernel.org/linux-mm/YhdWNLUhk+x9RAzU@yamatobi.andestech.com/
Link: https://lore.kernel.org/lkml/20220302065213.82702-1-alankao@andestech.com/
Link: https://www.andestech.com/en/products-solutions/andestar-architecture/
Signed-off-by: Alan Kao <alankao@andestech.com>
[arnd: rewrite changelog to provide more background]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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Signed-off-by: Christoph Hellwig <hch@lst.de>
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Since commit bcf9033e5449 ("sched: move CPU field back into thread_info
if THREAD_INFO_IN_TASK=y"), the CPU field in thread_info went back to
being managed by the core code, so we no longer have to keep it in sync
in arch code.
While at it, mark THREAD_INFO_IN_TASK as done for ARM in the
documentation.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
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This implements the CONFIG_THREAD_INFO_IN_TASK option.
With this change:
- before thread_info was part of the stack and located at the beginning of the stack
- now the thread_info struct is moved and located inside the task_struct structure
- the stack is allocated and handled like the major other platforms
- drop the cpu field of thread_info and use instead the one in task_struct
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sven Schnelle <svens@stackframe.org>
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/YN2nhV5F0hBVNPuX@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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