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

Will Deacon
2026-01-21T13:56:27Z

On Tue, Jan 20, 2026 at 05:59:47PM +0000, Yeoreum Yun wrote:
> On second thought, while a CPU that implements LSUI is unlikely to
> support AArch32 compatibility,
> I don't think LSUI requires the absence of AArch32.
> These two are independent features (and in fact our FVP reports/supports both).

Did you have to configure the FVP specially for this or that a "default"
configuration?

> Given that, I'm not sure a WARN is really necessary.
> Would it be sufficient to just drop the patch for swpX instead?

Given that the whole point of LSUI is to remove the PAN toggling, I think
we should make an effort to make sure that we don't retain PAN toggling
paths at runtime that could potentially be targetted by attackers. If we
drop the SWP emulation patch and then see that we have AArch32 at runtime,
we should forcefully disable the SWP emulation but, since we don't actually
think we're going to see this in practice, the WARN seemed simpler.

Will