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arm64/sve: Support vector length resetting for new processes

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It's desirable to be able to reset the vector length to some sane
default for new processes, since the new binary and its libraries
may or may not be SVE-aware.

This patch tracks the desired post-exec vector length (if any) in a
new thread member sve_vl_onexec, and adds a new thread flag
TIF_SVE_VL_INHERIT to control whether to inherit or reset the
vector length.  Currently these are inactive.  Subsequent patches
will provide the capability to configure them.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Dave Martin
2017-10-31 15:51:06 +00:00
committed by Will Deacon
parent bc0ee47603
commit 79ab047c75
3 changed files with 14 additions and 4 deletions
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16
arch/arm64/kernel/fpsimd.c
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@@ -111,6 +111,9 @@
*/
static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
/* Default VL for tasks that don't set it explicitly: */
static int sve_default_vl = SVE_VL_MIN;
/*
* Call __sve_free() directly only if you know task can't be scheduled
* or preempted.
@@ -474,15 +477,20 @@ void fpsimd_flush_thread(void)
* If a bug causes this to go wrong, we make some noise and
* try to fudge thread.sve_vl to a safe value here.
*/
vl = current->thread.sve_vl;
if (vl == 0)
vl = SVE_VL_MIN;
vl = current->thread.sve_vl_onexec ?
current->thread.sve_vl_onexec : sve_default_vl;
if (WARN_ON(!sve_vl_valid(vl)))
vl = SVE_VL_MIN;
current->thread.sve_vl = vl;
/*
* If the task is not set to inherit, ensure that the vector
* length will be reset by a subsequent exec:
*/
if (!test_thread_flag(TIF_SVE_VL_INHERIT))
current->thread.sve_vl_onexec = 0;
}
set_thread_flag(TIF_FOREIGN_FPSTATE);