Re: [PATCH v4 4/7] KVM: VMX: Implement LASS violation check

[Sean Christopherson <seanjc@google.com>]

On Mon, Sep 14, 2026, Sohil Mehta wrote:
> > 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.
> >
> 
> At first look, I found it a bit hard to follow as well. But instead of
> splitting out the logic into 4 static functions (which have limited
> value to the rest of the file), how about we add a high level comment on
> top of the function?

This is a great idea!
 
> I'll let Sean comment whether he prefers to change anything here or
> leave it as-is.
> 
> Note, some function names in the proposed diff could be misleading. For
> example, is_user_mode() checks the IMPLICIT flag in addition to the CPL
> which feels odd. And, is_lass_enforced() seems like a generic LASS check
> but in reality it only covers the supervisor data rule.

Yeah, this is my thinking as well.  In most cases, I would agree that we should
make the high-level concept as easy to follow as possible.  But helpers like
these, and even is_user_address() vs. is_supervisor_address(), highlight why I
think we should keep the more open-coded version in this particular case.  IMO,
the control flow isn't hard to follow because of poor coding/design, it's hard
to follow because the actual behavior of the CPU is complex and subtle.

So for me, this is more of a feature, not a bug.  I.e. I *want* to force readers
to slow down a bit, because while the basic gist is indeed very straightforward,
I think the resulting code is actively misleading if we bury the complexity and
subtlety in helpers.

That said, I love Sohil's idea of adding a function comment.  Someting along the
lines of "The basic flow is this: <example>, but the actual behavior is far more
subtle due to many exceptions and edge cases".