[PATCH v2 1/2] arm64: add an MTE support check to the top of mte_thread_switch()

[Peter Collingbourne]

On Wed, Sep 15, 2021 at 10:59 AM Catalin Marinas
<catalin.marinas at arm.com> wrote:
>
> On Tue, Sep 14, 2021 at 02:54:28PM -0700, Peter Collingbourne wrote:
> > This lets us avoid doing unnecessary work on hardware that does
> > not support MTE, and will allow us to freely use MTE instructions
> > in the code called by mte_thread_switch().
> >
> > Signed-off-by: Peter Collingbourne <pcc at google.com>
> > Link: https://linux-review.googlesource.com/id/I02fd000d1ef2c86c7d2952a7f099b254ec227a5d
> > ---
> >  arch/arm64/kernel/mte.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> > index 9d314a3bad3b..8fc2d90eeb00 100644
> > --- a/arch/arm64/kernel/mte.c
> > +++ b/arch/arm64/kernel/mte.c
> > @@ -199,6 +199,9 @@ void mte_thread_init_user(void)
> >
> >  void mte_thread_switch(struct task_struct *next)
> >  {
> > +     if (!system_supports_mte())
> > +             return;
> > +
> >       mte_update_sctlr_user(next);
>
> Ah, good point. While you are at this, could you please remove the
> system_supports_mte() check from mte_check_tfsr_el1() and add it to
> mte_check_tfsr_entry/exit? On the exit path, we unnecessarily do a
> dsb+isb even when MTE is not present.

Thanks for the suggestion. Done in v3.

Peter