x86: Don't support kernel-mode FPU with hardirqs disabled

This series returns to my earlier suggestion to make x86 not support kernel-mode FPU when hardirqs are disabled, aligning it with arm64
(https://lore.kernel.org/r/[email protected]).
To make this possible despite the use of the kernel-mode FPU functions by __save_processor_state() (which I mentioned at
https://lore.kernel.org/r/[email protected]), I've changed __save_processor_state() to use a new function instead of (mis)using the kernel-mode FPU functions.

This slightly reduces the overhead of kernel-mode FPU (since the result is fewer checks), and it fixes the issue reported at
https://lore.kernel.org/r/20250516112217.GBaCcf6Yoc6LkIIryP@fat_crate.local/
where irq_fpu_usable() incorrectly returned false during CPU initialization, causing a crash in the SHA-256 library code.

Eric Biggers (3):
x86/fpu: Add fpu_save_state() for __save_processor_state() x86/pm: Use fpu_save_state() in __save_processor_state() x86/fpu: Don't support kernel-mode FPU when irqs_disabled()

 arch/x86/include/asm/fpu/api.h |  1 +
 arch/x86/kernel/fpu/core.c     | 92 ++++++++++++++++++++--------------
 arch/x86/power/cpu.c           | 18 +++----
 3 files changed, 62 insertions(+), 49 deletions(-)

base-commit: 8566fc3b96539e3235909d6bdda198e1282beaed

2.49.0