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7df80a021f
commit 52f73c383b2418f2d31b798e765ae7d596c35021 upstream.
We detect the absence of FP/SIMD after an incapable CPU is brought up,
and by then we have kernel threads running already with TIF_FOREIGN_FPSTATE set
which could be set for early userspace applications (e.g, modprobe triggered
from initramfs) and init. This could cause the applications to loop forever in
do_nofity_resume() as we never clear the TIF flag, once we now know that
we don't support FP.
Fix this by making sure that we clear the TIF_FOREIGN_FPSTATE flag
for tasks which may have them set, as we would have done in the normal
case, but avoiding touching the hardware state (since we don't support any).
Also to make sure we handle the cases seemlessly we categorise the
helper functions to two :
1) Helpers for common core code, which calls into take appropriate
actions without knowing the current FPSIMD state of the CPU/task.
e.g fpsimd_restore_current_state(), fpsimd_flush_task_state(),
fpsimd_save_and_flush_cpu_state().
We bail out early for these functions, taking any appropriate actions
(e.g, clearing the TIF flag) where necessary to hide the handling
from core code.
2) Helpers used when the presence of FP/SIMD is apparent.
i.e, save/restore the FP/SIMD register state, modify the CPU/task
FP/SIMD state.
e.g,
fpsimd_save(), task_fpsimd_load() - save/restore task FP/SIMD registers
fpsimd_bind_task_to_cpu() \
- Update the "state" metadata for CPU/task.
fpsimd_bind_state_to_cpu() /
fpsimd_update_current_state() - Update the fp/simd state for the current
task from memory.
These must not be called in the absence of FP/SIMD. Put in a WARNING
to make sure they are not invoked in the absence of FP/SIMD.
KVM also uses the TIF_FOREIGN_FPSTATE flag to manage the FP/SIMD state
on the CPU. However, without FP/SIMD support we trap all accesses and
inject undefined instruction. Thus we should never "load" guest state.
Add a sanity check to make sure this is valid.
Fixes:
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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.