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arm64: neon: Remove support for nested or hardirq kernel-mode NEON

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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>
This commit is contained in:
Dave Martin 2017-08-03 17:23:23 +01:00 • committed by Catalin Marinas
parent 4328825d4f
commit cb84d11e16
6 changed files with 111 additions and 135 deletions
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56
arch/arm64/include/asm/fpsimdmacros.h
View file

@ -75,59 +75,3 @@
ldr w\tmpnr, [\state, #16 * 2 + 4]
fpsimd_restore_fpcr x\tmpnr, \state
.endm
.macro fpsimd_save_partial state, numnr, tmpnr1, tmpnr2
mrs x\tmpnr1, fpsr
str w\numnr, [\state, #8]
mrs x\tmpnr2, fpcr
stp w\tmpnr1, w\tmpnr2, [\state]
adr x\tmpnr1, 0f
add \state, \state, x\numnr, lsl #4
sub x\tmpnr1, x\tmpnr1, x\numnr, lsl #1
br x\tmpnr1
stp q30, q31, [\state, #-16 * 30 - 16]
stp q28, q29, [\state, #-16 * 28 - 16]
stp q26, q27, [\state, #-16 * 26 - 16]
stp q24, q25, [\state, #-16 * 24 - 16]
stp q22, q23, [\state, #-16 * 22 - 16]
stp q20, q21, [\state, #-16 * 20 - 16]
stp q18, q19, [\state, #-16 * 18 - 16]
stp q16, q17, [\state, #-16 * 16 - 16]
stp q14, q15, [\state, #-16 * 14 - 16]
stp q12, q13, [\state, #-16 * 12 - 16]
stp q10, q11, [\state, #-16 * 10 - 16]
stp q8, q9, [\state, #-16 * 8 - 16]
stp q6, q7, [\state, #-16 * 6 - 16]
stp q4, q5, [\state, #-16 * 4 - 16]
stp q2, q3, [\state, #-16 * 2 - 16]
stp q0, q1, [\state, #-16 * 0 - 16]
0:
.endm
.macro fpsimd_restore_partial state, tmpnr1, tmpnr2
ldp w\tmpnr1, w\tmpnr2, [\state]
msr fpsr, x\tmpnr1
fpsimd_restore_fpcr x\tmpnr2, x\tmpnr1
adr x\tmpnr1, 0f
ldr w\tmpnr2, [\state, #8]
add \state, \state, x\tmpnr2, lsl #4
sub x\tmpnr1, x\tmpnr1, x\tmpnr2, lsl #1
br x\tmpnr1
ldp q30, q31, [\state, #-16 * 30 - 16]
ldp q28, q29, [\state, #-16 * 28 - 16]
ldp q26, q27, [\state, #-16 * 26 - 16]
ldp q24, q25, [\state, #-16 * 24 - 16]
ldp q22, q23, [\state, #-16 * 22 - 16]
ldp q20, q21, [\state, #-16 * 20 - 16]
ldp q18, q19, [\state, #-16 * 18 - 16]
ldp q16, q17, [\state, #-16 * 16 - 16]
ldp q14, q15, [\state, #-16 * 14 - 16]
ldp q12, q13, [\state, #-16 * 12 - 16]
ldp q10, q11, [\state, #-16 * 10 - 16]
ldp q8, q9, [\state, #-16 * 8 - 16]
ldp q6, q7, [\state, #-16 * 6 - 16]
ldp q4, q5, [\state, #-16 * 4 - 16]
ldp q2, q3, [\state, #-16 * 2 - 16]
ldp q0, q1, [\state, #-16 * 0 - 16]
0:
.endm