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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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Deepak Gupta
cd24f44050
csr_sscratch CSR holds current task_struct address when hart is in user
space. Trap handler on entry spills csr_sscratch into "tp" (x2) register
and zeroes out csr_sscratch CSR. Trap handler on exit reloads "tp" with
expected user mode value and place current task_struct address again in
csr_sscratch CSR.
This patch assumes "tp" is pointing to task_struct. If value in
csr_sscratch is numerically greater than "tp" then it assumes csr_sscratch
is correct address of current task_struct. This logic holds when
- hart is in user space, "tp" will be less than csr_sscratch.
- hart is in kernel space but not in trap handler, "tp" will be more
than csr_sscratch (csr_sscratch being equal to 0).
- hart is executing trap handler
- "tp" is still pointing to user mode but csr_sscratch contains
ptr to task_struct. Thus numerically higher.
- "tp" is pointing to task_struct but csr_sscratch now contains
either 0 or numerically smaller value (transiently holds
user mode tp)
Link: https://lkml.kernel.org/r/20231026233837.612405-1-debug@rivosinc.com
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Tested-by: Hsieh-Tseng Shen <woodrow.shen@sifive.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Glenn Washburn <development@efficientek.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Jeff Xie <xiehuan09@gmail.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.