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feec6cd973
[ Upstream commit 1937e18cc3cf27e2b3ef70e8c161437051ab7608 ]
Ongoing work on an optimization to batch-preallocate vCPU state buffers
for KVM revealed a mismatch between the allocation sizes used in
fpu_alloc_guest_fpstate() and fpstate_realloc(). While the former
allocates a buffer sized to fit the default set of XSAVE features
in UABI form (as per fpu_user_cfg), the latter uses its ksize argument
derived (for the requested set of features) in the same way as the sizes
found in fpu_kernel_cfg, i.e. using the compacted in-kernel
representation.
The correct size to use for guest FPU state should indeed be the
kernel one as seen in fpstate_realloc(). The original issue likely
went unnoticed through a combination of UABI size typically being
larger than or equal to kernel size, and/or both amounting to the
same number of allocated 4K pages.
Fixes: 69f6ed1d14 ("x86/fpu: Provide infrastructure for KVM FPU cleanup")
Signed-off-by: Stanislav Spassov <stanspas@amazon.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250218141045.85201-1-stanspas@amazon.de
Signed-off-by: Sasha Levin <sashal@kernel.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.