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.
--
Catalin
