Re: [PATCH v2 0/3] x86: Extend LASS support to EFI configurations

[Luck, Tony]

On Tue, Jan 20, 2026 at 03:47:27PM -0800, Sohil Mehta wrote:
> Linear Address Space Separation (LASS) is currently disabled [1] when
> support for vsyscall emulation or EFI is compiled in. This series
> extends LASS support to EFI-enabled configurations.

I tried these patches on a LASS-capable system with a kernel built with
CONFIG_X86_VSYSCALL_EMULATION disabled, and traces added to efi_disable_lass()
and efi_enable_lass().

System boots OK (with a bunch of my trace messages showing that CR4.LASS
was disabled/enabled around EFI calls from several CPUs).

Just for grins I commented out the CR4 changes from the efi_disable_lass()
and efi_enable_lass(). System still boots OK, so it seems the EFI runtime
calls during boot don't have any of the BIOS bugs that require LASS disable.

Tested-by: Tony Luck <tony.luck@xxxxxxxxx>

-Tony