Subject: Re: (subset) [PATCH v17 0/8] support FEAT_LSUI

From: Catalin Marinas <[email-masked]>
Date: Fri, 27 Mar 2026 17:18:31 +0000

On Fri, Mar 27, 2026 at 01:56:11PM +0000, Yeoreum Yun wrote:
> > I decided to drop patch [6/8] (arm64: armv8_deprecated: disable swp
> > emulation when FEAT_LSUI present). The way FEAT_LSUI support looks now,
> > we still have uaccess_enable_privileged() working properly and we could
> > even support SWP emulation using exclusives. While it's highly unlikely
> > to see both 32-bit EL0 and FEAT_LSUI in practice,
> 
> This is one of decisive reason to drop the swp emulation with LSUI
> (https://lore.kernel.org/all/aXDbBKhE1SdCW6q4@willie-the-truck/)

Ah, I forgot about this discussion. It's a valid point, I just thought
it's unnecessary given that __uaccess_disable_hw_pan() still works.

If we want strict no PAN, I can add it back (really small patch). I
wonder whether we should also add a
WARN_ON_ONCE(cpus_have_final_cap(ARM64_HAS_LSUI)) to the pan disabling
function. Not urgent though.

-- 
Catalin