On Mon, Jul 20, 2020 at 06:00:50PM +0100, Dave P Martin wrote:

On Mon, Jul 20, 2020 at 04:30:35PM +0100, Kevin Brodsky wrote:

quoted

On 15/07/2020 18:08, Catalin Marinas wrote:

quoted

+void mte_thread_switch(struct task_struct *next)
+{
+	if (!system_supports_mte())
+		return;
+
+	/* avoid expensive SCTLR_EL1 accesses if no change */
+	if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)

I think this could be improved by checking whether `next` is a kernel
thread, in which case thread.sctlr_tcf0 is 0 but there is no point in
setting SCTLR_EL1.TCF0, since there should not be any access via TTBR0.

Out of interest, do we have a nice way of testing for a kernel thread
now?

I remember fpsimd_thread_switch() used to check for task->mm, but we
seem to have got rid of that at some point.  set_mm() can defeat this,
and anyway the heavy lifting for FPSIMD is now deferred until returning
to userspace.

I think a better way is (current->flags & PF_KTHREAD). kthread_use_mm()
indeed changes current->mm.

-- 
Catalin

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel