arm64/sve: Refactor user SVE trap maintenance for external use (0cff8e77) · Commits · 戴 / test

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:

Dave Martin <Dave.Martin@arm.com> Reviewed-by:

Alex Bennée <alex.bennee@linaro.org> Acked-by:

Marc Zyngier <marc.zyngier@arm.com> Acked-by:

Catalin Marinas <catalin.marinas@arm.com> Signed-off-by:

Marc Zyngier <marc.zyngier@arm.com>

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();
		}

Admin message