[PATCH v8 0/4] arm64: mte: allow async MTE to be upgraded to sync on a per-CPU basis

[Peter Collingbourne]

On Thu, Jul 1, 2021 at 10:10 AM Catalin Marinas <catalin.marinas at arm.com> wrote:
>
> On Wed, Jun 30, 2021 at 04:15:05PM -0700, Peter Collingbourne wrote:
> > On some CPUs the performance of MTE in synchronous mode is similar
> > to that of asynchronous mode. This makes it worthwhile to enable
> > synchronous mode on those CPUs when asynchronous mode is requested,
> > in order to gain the error detection benefits of synchronous mode
> > without the performance downsides. Therefore, make it possible for
> > user programs to opt into upgrading to synchronous mode on those CPUs.
> >
> > This is done by introducing a notion of a preferred TCF mode, which is
> > controlled on a per-CPU basis by a sysfs node. The existing SYNC and
> > ASYNC TCF settings are repurposed as bitfields that specify a set of
> > possible modes. If the preferred TCF mode for a particular CPU is in
> > the user-provided mode set (this will always be the case for mode sets
> > containing more than one mode because the kernel only supports two tag
> > checking modes, but future kernels may support more modes) then that
> > mode is used when running on that CPU, otherwise one of the modes in
> > the task's mode set will be selected in a currently unspecified manner.
>
> The series looks good to me but please post it again after -rc1 if it
> doesn't apply cleanly.

Thanks. I tried applying this series to linux-next and it applied
cleanly, so it seems likely that it will apply cleanly to rc1. I will
let you know if that is not the case though.

I received feedback elsewhere that we should be adding documentation
under Documentation/ABI for the new sysfs node. Also while developing
my GCR on task switch patch I noticed a small cleanup that could be
made to patch 2 of this series. I went ahead and made both of those
improvements in v9.

Peter