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cdb4ce96fd
commit e45122893a9870813f9bd7b4add4f613e6f29008 upstream.
Currently, requesting kernel FPU access doesn't distinguish which parts of
the extended ("FPU") state are needed. This is nice for simplicity, but
there are a few cases in which it's suboptimal:
- The vast majority of in-kernel FPU users want XMM/YMM/ZMM state but do
not use legacy 387 state. These users want MXCSR initialized but don't
care about the FPU control word. Skipping FNINIT would save time.
(Empirically, FNINIT is several times slower than LDMXCSR.)
- Code that wants MMX doesn't want or need MXCSR initialized.
_mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and
initializing MXCSR will fail because LDMXCSR generates an #UD when the
aforementioned CR4 bit is not set.
- Any future in-kernel users of XFD (eXtended Feature Disable)-capable
dynamic states will need special handling.
Add a more specific API that allows callers to specify exactly what they
want.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Krzysztof Piotr Olędzki <ole@ans.pl>
Link: https://lkml.kernel.org/r/aff1cac8b8fc7ee900cf73e8f2369966621b053f.1611205691.git.luto@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
77 lines
2.1 KiB
C
77 lines
2.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 1994 Linus Torvalds
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*
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* Pentium III FXSR, SSE support
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* General FPU state handling cleanups
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* Gareth Hughes <gareth@valinux.com>, May 2000
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* x86-64 work by Andi Kleen 2002
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*/
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#ifndef _ASM_X86_FPU_API_H
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#define _ASM_X86_FPU_API_H
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#include <linux/bottom_half.h>
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/*
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* Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
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* disables preemption so be careful if you intend to use it for long periods
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* of time.
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* If you intend to use the FPU in irq/softirq you need to check first with
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* irq_fpu_usable() if it is possible.
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*/
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/* Kernel FPU states to initialize in kernel_fpu_begin_mask() */
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#define KFPU_387 _BITUL(0) /* 387 state will be initialized */
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#define KFPU_MXCSR _BITUL(1) /* MXCSR will be initialized */
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extern void kernel_fpu_begin_mask(unsigned int kfpu_mask);
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extern void kernel_fpu_end(void);
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extern bool irq_fpu_usable(void);
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extern void fpregs_mark_activate(void);
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/* Code that is unaware of kernel_fpu_begin_mask() can use this */
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static inline void kernel_fpu_begin(void)
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{
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kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR);
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}
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/*
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* Use fpregs_lock() while editing CPU's FPU registers or fpu->state.
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* A context switch will (and softirq might) save CPU's FPU registers to
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* fpu->state and set TIF_NEED_FPU_LOAD leaving CPU's FPU registers in
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* a random state.
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*/
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static inline void fpregs_lock(void)
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{
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preempt_disable();
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local_bh_disable();
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}
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static inline void fpregs_unlock(void)
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{
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local_bh_enable();
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preempt_enable();
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}
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#ifdef CONFIG_X86_DEBUG_FPU
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extern void fpregs_assert_state_consistent(void);
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#else
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static inline void fpregs_assert_state_consistent(void) { }
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#endif
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/*
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* Load the task FPU state before returning to userspace.
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*/
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extern void switch_fpu_return(void);
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/*
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* Query the presence of one or more xfeatures. Works on any legacy CPU as well.
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*
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* If 'feature_name' is set then put a human-readable description of
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* the feature there as well - this can be used to print error (or success)
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* messages.
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*/
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extern int cpu_has_xfeatures(u64 xfeatures_mask, const char **feature_name);
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#endif /* _ASM_X86_FPU_API_H */
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