Re: [PATCH v2 1/2] arm64/signal: Restore TPIDR2 register rather than memory state

[Mark Brown <broonie@kernel.org>]

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On Fri, Jun 23, 2023 at 06:28:12PM +0100, Catalin Marinas wrote:
> On Thu, Jun 22, 2023 at 06:11:20PM +0100, Mark Brown wrote:

> > TPIDR2 is intended to go along with the thread stack, it's intended to
> > be used to allow lazy save of the (rather large) ZA register state when
> > a called function needs it rather than forcing it to be caller saved.
> > TPIDR2 is used to point to memory allocated for managing this process,
> > something that provides a new value should be making a deliberate
> > decision to do so and editing the stack frame.

> OK, so if the signal handler invokes a function that touches the ZA
> state, it may use TPIDR2 for lazy saving in any callee. In this case we
> need to restore the original TPIDR2 of the interrupted context on
> sigreturn.

Yeah, or if something tries to sigreturn to a previously saved context
which had live TPIDR2 state things might end up unfortunate.

> So I convinced myself this is the only option that makes sense ;). I'll
> queue the patches.

Thanks.

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