Re: [PATCH v11 RESEND 9/9] arm64: armv8_deprecated: apply FEAT_LSUI for swpX emulation.

Yeoreum Yun
2025-12-15T09:57:19Z

Hi,

> On Sun, 14 Dec 2025 11:22:48 +0000,
> Yeoreum Yun <yeoreum.yun@arm.com> wrote:
> >
> > Apply the FEAT_LSUI instruction to emulate the deprecated swpX
> > instruction, so that toggling of the PSTATE.PAN bit can be removed when
> > LSUI-related instructions are used.
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
>
> It really begs the question: what are the odds of ever seeing a CPU
> that implements both LSUI and AArch32?
>
> This seems extremely unlikely to me.

Well, I'm not sure how many CPU will have
both ID_AA64PFR0_EL1.EL0 bit as 0b0010 and FEAT_LSUI
(except FVP currently) -- at least the CPU what I saw,
most of them set ID_AA64PFR0_EL1.EL0 as 0b0010.

If you this seems useless, I don't have any strong comments
whether drop patches related to deprecated swp instruction parts
(patch 8-9 only) or not.
(But, I hope to pass this decision to maintaining perspective...)

>
> M.
>
> --
> Without deviation from the norm, progress is not possible.

--
Sincerely,
Yeoreum Yun