[PATCH] arm64: mte: Make mte_check_tfsr_*() conditional on KASAN instead of MTE

[Peter Collingbourne]

On Tue, May 28, 2024 at 3:51 PM Peter Collingbourne <pcc at google.com> wrote:
>
> The check in mte_check_tfsr_el1() is only necessary if HW tag
> based KASAN is enabled. However, we were also executing the check
> if MTE is enabled and KASAN is enabled at build time but disabled
> at runtime. This turned out to cause a measurable increase in
> power consumption on a specific microarchitecture after enabling
> MTE. Moreover, on the same system, an increase in invalid syscall
> latency (as measured by [1]) of around 20-30% (depending on the
> cluster) was observed after enabling MTE; this almost entirely goes
> away after removing this check. Therefore, make the check conditional
> on whether KASAN is enabled rather than on whether MTE is enabled.

Ping.

Peter