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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>
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Dave Martin authored and Will Deacon committed Nov 3, 2017
1 parent bc0ee47 commit 79ab047
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Showing 3 changed files with 14 additions and 4 deletions.
1 change: 1 addition & 0 deletions arch/arm64/include/asm/processor.h
Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,7 @@ struct thread_struct {
struct fpsimd_state fpsimd_state;
void *sve_state; /* SVE registers, if any */
unsigned int sve_vl; /* SVE vector length */
unsigned int sve_vl_onexec; /* SVE vl after next exec */
unsigned long fault_address; /* fault info */
unsigned long fault_code; /* ESR_EL1 value */
struct debug_info debug; /* debugging */
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1 change: 1 addition & 0 deletions arch/arm64/include/asm/thread_info.h
Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,7 @@ void arch_release_task_struct(struct task_struct *tsk);
#define TIF_SINGLESTEP 21
#define TIF_32BIT 22 /* 32bit process */
#define TIF_SVE 23 /* Scalable Vector Extension in use */
#define TIF_SVE_VL_INHERIT 24 /* Inherit sve_vl_onexec across exec */

#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
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16 changes: 12 additions & 4 deletions arch/arm64/kernel/fpsimd.c
Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand Down Expand Up @@ -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);
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