Re: [PATCH v11 9/9] x86/cpu: Enable LASS by default during CPU initialization

Andy Lutomirski
2025-10-30T17:32:19Z

On Thu, Oct 30, 2025, at 10:24 AM, Sohil Mehta wrote:
> On 10/30/2025 9:53 AM, Andy Lutomirski wrote:
>
>>> On the other hand, supporting EMULATE mode during a #GP is a bit tricky,
>>> which isn't worth the effort.
>>
>> I would say it's definitely worth the effort, but it probably does make sense to get the rest of the series in a mergeable condition such that it only works with vsyscall=none.
>
> I meant the full emulation mode where the Vsyscall page is readable. It
> is only available via vsyscall=emulate. No one should be using that one,
> right?
>
> I thought you and Linus agreed on removing EMULATE mode completely:
> https://lore.kernel.org/all/CALCETrXHJ7837+cmahg-wjR3iRHbDJ6JtVGaoDFC4dx-L8r8OA@mail.gmail.com/
>
> I agree that it would be worthwhile (and relatively easy) to support the
> execute (XONLY) mode (that only does instruction fetches). That is what
> the separate vsyscall series would do once the LASS base is in.

Ah, I misunderstood you. I agree.