Hi Catalin,
> On Fri, Feb 27, 2026 at 03:17:04PM +0000, Yeoreum Yun wrote:
> > +static int __lsui_swap_desc(u64 __user *ptep, u64 old, u64 new)
> > +{
> > + u64 tmp = old;
> > + int ret = 0;
> > +
> > + /*
> > + * FEAT_LSUI is supported since Armv9.6, where FEAT_PAN is mandatory.
> > + * However, this assumption may not always hold:
> > + *
> > + * - Some CPUs advertise FEAT_LSUI but lack FEAT_PAN.
> > + * - Virtualisation or ID register overrides may expose invalid
> > + * feature combinations.
> > + *
> > + * Rather than disabling FEAT_LSUI when FEAT_PAN is absent, wrap LSUI
> > + * instructions with uaccess_ttbr0_enable()/disable() when
> > + * ARM64_SW_TTBR0_PAN is enabled.
> > + */
> > + uaccess_ttbr0_enable();
> > +
> > + asm volatile(__LSUI_PREAMBLE
>
> I haven't tried, so just asking. Does the toolchain complain if it does
> not support LSUI or is this path eliminated (due to
> cpucap_is_possible()) before being handed over to gas? It's probably
> fine but worth checking.
Yes I did with clang-19 and that's one of v14's modification:
- https://lore.kernel.org/all/[email protected]/
--
Sincerely,
Yeoreum Yun
