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cb84d11e16
Support for kernel-mode NEON to be nested and/or used in hardirq
context adds significant complexity, and the benefits may be
marginal. In practice, kernel-mode NEON is not used in hardirq
context, and is rarely used in softirq context (by certain mac80211
drivers).
This patch implements an arm64 may_use_simd() function to allow
clients to check whether kernel-mode NEON is usable in the current
context, and simplifies kernel_neon_{begin,end}() to handle only
saving of the task FPSIMD state (if any). Without nesting, there
is no other state to save.
The partial fpsimd save/restore functions become redundant as a
result of these changes, so they are removed too.
The save/restore model is changed to operate directly on
task_struct without additional percpu storage. This simplifies the
code and saves a bit of memory, but means that softirqs must now be
disabled when manipulating the task fpsimd state from task context:
correspondingly, preempt_{en,dis}sable() calls are upgraded to
local_bh_{en,dis}able() as appropriate. fpsimd_thread_switch()
already runs with hardirqs disabled and so is already protected
from softirqs.
These changes should make it easier to support kernel-mode NEON in
the presence of the Scalable Vector extension in the future.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
78 lines
2.3 KiB
C
78 lines
2.3 KiB
C
/*
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* FP/SIMD state saving and restoring macros
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*
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* Copyright (C) 2012 ARM Ltd.
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* Author: Catalin Marinas <catalin.marinas@arm.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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.macro fpsimd_save state, tmpnr
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stp q0, q1, [\state, #16 * 0]
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stp q2, q3, [\state, #16 * 2]
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stp q4, q5, [\state, #16 * 4]
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stp q6, q7, [\state, #16 * 6]
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stp q8, q9, [\state, #16 * 8]
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stp q10, q11, [\state, #16 * 10]
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stp q12, q13, [\state, #16 * 12]
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stp q14, q15, [\state, #16 * 14]
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stp q16, q17, [\state, #16 * 16]
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stp q18, q19, [\state, #16 * 18]
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stp q20, q21, [\state, #16 * 20]
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stp q22, q23, [\state, #16 * 22]
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stp q24, q25, [\state, #16 * 24]
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stp q26, q27, [\state, #16 * 26]
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stp q28, q29, [\state, #16 * 28]
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stp q30, q31, [\state, #16 * 30]!
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mrs x\tmpnr, fpsr
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str w\tmpnr, [\state, #16 * 2]
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mrs x\tmpnr, fpcr
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str w\tmpnr, [\state, #16 * 2 + 4]
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.endm
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.macro fpsimd_restore_fpcr state, tmp
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/*
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* Writes to fpcr may be self-synchronising, so avoid restoring
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* the register if it hasn't changed.
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*/
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mrs \tmp, fpcr
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cmp \tmp, \state
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b.eq 9999f
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msr fpcr, \state
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9999:
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.endm
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/* Clobbers \state */
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.macro fpsimd_restore state, tmpnr
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ldp q0, q1, [\state, #16 * 0]
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ldp q2, q3, [\state, #16 * 2]
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ldp q4, q5, [\state, #16 * 4]
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ldp q6, q7, [\state, #16 * 6]
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ldp q8, q9, [\state, #16 * 8]
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ldp q10, q11, [\state, #16 * 10]
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ldp q12, q13, [\state, #16 * 12]
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ldp q14, q15, [\state, #16 * 14]
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ldp q16, q17, [\state, #16 * 16]
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ldp q18, q19, [\state, #16 * 18]
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ldp q20, q21, [\state, #16 * 20]
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ldp q22, q23, [\state, #16 * 22]
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ldp q24, q25, [\state, #16 * 24]
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ldp q26, q27, [\state, #16 * 26]
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ldp q28, q29, [\state, #16 * 28]
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ldp q30, q31, [\state, #16 * 30]!
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ldr w\tmpnr, [\state, #16 * 2]
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msr fpsr, x\tmpnr
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ldr w\tmpnr, [\state, #16 * 2 + 4]
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fpsimd_restore_fpcr x\tmpnr, \state
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.endm
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