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Commit 0cff8e77 authored by Dave Martin's avatar Dave Martin Committed by Marc Zyngier
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arm64/sve: Refactor user SVE trap maintenance for external use 



In preparation for optimising the way KVM manages switching the
guest and host FPSIMD state, it is necessary to provide a means for
code outside arch/arm64/kernel/fpsimd.c to restore the user trap
configuration for SVE correctly for the current task.

Rather than requiring external code to duplicate the maintenance
explicitly, this patch moves the trap maintenenace to
fpsimd_bind_to_cpu(), since it is logically part of the work of
associating the current task with the cpu.

Because fpsimd_bind_to_cpu() is rather a cryptic name to publish
alongside fpsimd_bind_state_to_cpu(), the former function is
renamed to fpsimd_bind_task_to_cpu() to make its purpose more
explicit.

This patch makes appropriate changes to ensure that
fpsimd_bind_task_to_cpu() is always called alongside
task_fpsimd_load(), so that the trap maintenance continues to be
done in every situation where it was done prior to this patch.

As a side-effect, the metadata updates done by
fpsimd_bind_task_to_cpu() now change from conditional to
unconditional in the "already bound" case of sigreturn.  This is
harmless, and a couple of extra stores on this slow path will not
impact performance.  I consider this a reasonable price to pay for
a slightly cleaner interface.

Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Acked-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent df3fb968

arch/arm64/kernel/fpsimd.c

+15 −15
Original line number Diff line number Diff line
@@ -257,16 +257,6 @@ static void task_fpsimd_load(void) 
			       sve_vq_from_vl(current->thread.sve_vl) - 1);

	else

		fpsimd_load_state(&current->thread.uw.fpsimd_state);



	if (system_supports_sve()) {

		/* Toggle SVE trapping for userspace if needed */

		if (test_thread_flag(TIF_SVE))

			sve_user_enable();

		else

			sve_user_disable();



		/* Serialised by exception return to user */

	}

}



/*
@@ -278,7 +268,7 @@ static void task_fpsimd_load(void) 
static void fpsimd_save(void)

{

	struct user_fpsimd_state *st = __this_cpu_read(fpsimd_last_state.st);

	/* set by fpsimd_bind_to_cpu() */

	/* set by fpsimd_bind_task_to_cpu() */



	WARN_ON(!in_softirq() && !irqs_disabled());
@@ -996,7 +986,7 @@ void fpsimd_signal_preserve_current_state(void) 
 * Associate current's FPSIMD context with this cpu

 * Preemption must be disabled when calling this function.

 */

static void fpsimd_bind_to_cpu(void)

static void fpsimd_bind_task_to_cpu(void)

{

	struct fpsimd_last_state_struct *last =

		this_cpu_ptr(&fpsimd_last_state);
@@ -1004,6 +994,16 @@ static void fpsimd_bind_to_cpu(void) 
	last->st = &current->thread.uw.fpsimd_state;

	last->sve_in_use = test_thread_flag(TIF_SVE);

	current->thread.fpsimd_cpu = smp_processor_id();



	if (system_supports_sve()) {

		/* Toggle SVE trapping for userspace if needed */

		if (test_thread_flag(TIF_SVE))

			sve_user_enable();

		else

			sve_user_disable();



		/* Serialised by exception return to user */

	}

}



/*
@@ -1020,7 +1020,7 @@ void fpsimd_restore_current_state(void) 


	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {

		task_fpsimd_load();

		fpsimd_bind_to_cpu();

		fpsimd_bind_task_to_cpu();

	}



	local_bh_enable();
@@ -1043,9 +1043,9 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state) 
		fpsimd_to_sve(current);



	task_fpsimd_load();

	fpsimd_bind_task_to_cpu();



	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE))

		fpsimd_bind_to_cpu();

	clear_thread_flag(TIF_FOREIGN_FPSTATE);



	local_bh_enable();

}