Re: [PATCH v11 5/9] x86/efi: Disable LASS while mapping the EFI runtime services

Sohil Mehta
2025-10-31T18:03:21Z

On 10/31/2025 10:41 AM, Dave Hansen wrote:
> On 10/31/25 10:38, Andy Lutomirski wrote:
>> Am I imagining an issue that doesn’t exist? Is there some way to be
>> reasonably convinced that you haven’t missed another EFI code path?
>> Would it be ridiculous to defer enabling LASS until we’re almost
>> ready to run user code?

> Deferring is a good idea. I was just asking for the same thing for the
> CR pinning enforcement. The earlier we try to do these things, the more
> we just trip over ourselves.

I had suggested deferring as well to Kirill when I was reviewing the
series. He preferred to enable LASS with other similar features such as
SMAP, SMEP.

One other thing to consider:

Doing it in identify_cpu() makes it easy for all the APs to program
their CR4.LASS bit. If we were to defer it, we would need some
additional work to setup all the APs.

Do we already do this for something else? That would make it easier to
tag along.