On 8/5/2026 6:15 PM, Sohil Mehta wrote:
> 
> +bool vmx_is_lass_violation(struct kvm_vcpu *vcpu, gva_t gva,
> +			   unsigned int size, unsigned int flags)
> +{
> +	const bool is_supervisor_address = !!(gva & BIT_ULL(63));
> +	const bool implicit_supervisor = !!(flags & X86EMUL_F_IMPLICIT);
> +	const bool fetch = !!(flags & X86EMUL_F_FETCH);
> +
> +	if (!kvm_is_cr4_bit_set(vcpu, X86_CR4_LASS) || !is_long_mode(vcpu))
> +		return false;
> +
> +	/*
> +	 * INVLPG isn't subject to LASS, e.g. to allow invalidating userspace
> +	 * addresses without toggling RFLAGS.AC.  Branch targets aren't subject
> +	 * to LASS in order to simplify far control transfers (the subsequent
> +	 * fetch will enforce LASS as appropriate).
> +	 */
> +	if (flags & (X86EMUL_F_BRANCH | X86EMUL_F_INVLPG))
> +		return false;
> +
> +	if (!implicit_supervisor && vmx_get_cpl(vcpu) == 3)
> +		return is_supervisor_address;
> +
> +	/*
> +	 * LASS enforcement for supervisor-mode data accesses depends on SMAP
> +	 * being enabled, and like SMAP ignores explicit accesses if RFLAGS.AC=1.
> +	 */
> +	if (!fetch) {
> +		if (!kvm_is_cr4_bit_set(vcpu, X86_CR4_SMAP))
> +			return false;
> +
> +		if (!implicit_supervisor && (kvm_get_rflags(vcpu) & X86_EFLAGS_AC))
> +			return false;
> +	}
> +
> +	/*
> +	 * The entire access must be in the appropriate address space.  Note,
> +	 * if LAM is supported, @gva has already been untagged, so barring a
> +	 * massive architecture change to expand the canonical address range,
> +	 * it's impossible for a user access to straddle user and supervisor
> +	 * address spaces.
> +	 */
> +	if (size && !((gva + size - 1) & BIT_ULL(63)))
> +		return true;
> +
> +	return !is_supervisor_address;
> +}

This looks like an essential piece for the check introduced in the 
series. I could follow the logic, and it looks sane to me. If allowed,

   Reviewed-by: Chang S. Bae <chang.seok.bae@intel.com>

The code also looks to be written according to Sean's comment in:

   https://lore.kernel.org/kvm/ZNwOYdy3AC12MI52@google.com

Yes, this could be a matter of taste as taking and going to maintain the 
code. But as a reader looking at this, the logic was not that easy to 
capture at a high level.

So what the the bottom half code does seems to be something like:

   if in user mode,
       violated if gva is a supervisor address

   if in supervisor mode,
       if LASS enforcement is applicable,
           violated if either gva or its access end is an user address

Maybe the high-level logic could be highlighted first. Attached a diff 
to help figuring out that option just in case. Feel free to ignore if it 
doesn't matter that much.

Thanks,
Chang