Re: [PATCH 0/5] target/i386: Add support for LASS

[Binbin Wu <binbin.wu@linux.intel.com>]

On 8/26/2026 11:57 AM, Kishen Maloor wrote:
> This series adds QEMU support for Linear Address Space Separation (LASS) [1],
> an Intel security feature that prevents a class of side-channel attacks
> relying on speculative accesses across the user/kernel boundary. Paging,
> along with SMEP and SMAP, already provides mode-based access protection,
> but enforcing it requires a page walk whose timing can leak the layout of
> kernel memory. LASS applies the equivalent protections during
> linear-address pre-processing: given the usual partitioning of the linear
> address space into a user half (bit 63 clear) and a supervisor half
> (bit 63 set), an access targeting the opposite half is rejected on the
> basis of bit 63 alone, before any page walk.
> 
> This series enumerates the LASS CPUID bit, recognizes CR4.LASS,
> and exposes LASS on the relevant Intel CPU models via new versioned models.
> LASS is not emulated by TCG.
> 
> Exposing LASS to a guest also requires KVM support: KVM must validate
> the CPUID bit and CR4.LASS, and enforce LASS violations in its
> instruction emulator. That enabling is currently under review [2].
> 
> Tested with a Linux guest on LASS-capable hardware: LASS is enumerated and
> CR4.LASS is set under KVM, and not enumerated under TCG.
> 
> [1] Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A,
>     Section 4.3, "Linear-Address-Space Separation (LASS)".
> [2] https://lore.kernel.org/kvm/20260806011536.4172258-1-sohil.mehta@intel.com/
> 
> Isaku Yamahata (2):
>   target/i386: Add support for LASS in CPUID enumeration
>   target/i386: Add LASS support in CR4
> 
> Kishen Maloor (3):
>   target/i386: Introduce DiamondRapids-v3 to enable LASS
>   target/i386: Introduce SierraForest-v7 to enable LASS
>   target/i386: Introduce ClearwaterForest-v5 to enable LASS

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>

> 
>  target/i386/cpu.c    | 26 +++++++++++++++++++++++++-
>  target/i386/cpu.h    |  7 ++++++-
>  target/i386/helper.c |  4 ++++
>  3 files changed, 35 insertions(+), 2 deletions(-)
>