[PATCH v2] arm64: Implement prctl(PR_{G,S}ET_TSC)

[Will Deacon]

Hi Peter,

On Mon, Jun 10, 2024 at 01:24:51PM -0700, Peter Collingbourne wrote:
> On Fri, May 17, 2024 at 2:25 PM Peter Collingbourne <pcc at google.com> wrote:
> >
> > On arm64, this prctl controls access to CNTVCT_EL0, CNTVCTSS_EL0 and
> > CNTFRQ_EL0 via CNTKCTL_EL1.EL0VCTEN. Since this bit is also used to
> > implement various erratum workarounds, check whether the CPU needs
> > a workaround whenever we potentially need to change it.
> 
> Ping.

Chatting with Marc and Catalin about this, we're a little uneasy about
exposing a prctl() for this. Ptrace does seem like a much better fit.
Can you add a new regset for the counter instead?

Will