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@xxxxxxx>
Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
Changes since v10:
Requested by Alex Bennée:
* Amend comment about the source of fpsimd_last_state.st in fpsimd_save().
---
arch/arm64/kernel/fpsimd.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index d736b6c..d5f659f 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -257,16 +257,6 @@ static void task_fpsimd_load(void)
sve_vq_from_vl(current->thread.sve_vl) - 1);
else
fpsimd_load_state(¤t->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 = ¤t->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();
}
--
2.1.4
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