Re: [RFCv2 00/10] Linear Address Masking enabling

Thomas Gleixner
2022-05-12T19:31:31Z

On Thu, May 12 2022 at 19:56, Kirill A. Shutemov wrote:
> On Thu, May 12, 2022 at 05:42:58PM +0200, Thomas Gleixner wrote:
>> On Wed, May 11 2022 at 08:49, Peter Zijlstra wrote:
>> > On Wed, May 11, 2022 at 05:27:40AM +0300, Kirill A. Shutemov wrote:
>> > So aren't we creating a problem with LAM_U48 where programs relying on
>> > it are of limited sustainability?
>> >
>> > Any such program simply *cannot* run on 5 level pagetables. Why do we
>> > want to do this?
>>
>> More bits are better :)
>>
>> Seriously, I agree that restricting it to LAM57, which gives us 6 bits,
>> makes a lot of sense _and_ makes the whole thing way simpler.
>>
>> So supporting both needs a truly good justification and a real world use
>> case.
>
> I asked the question before[1]. Basically, more bits more better:
>
> For HWASAN #bits == detection probability.
> For MarkUS #bits == exponential cost reduction

What is MarkUS? It's not really helpful to provide acronyms which are
not decodable.

> I would really like to have only LAM_U57, but IIUC 6 bits is not always
> enough.
>
> Dmitry, could you elaborate?
>
> [1] https://mobile.twitter.com/dvyukov/status/1342019823400837120

I don't know whether he reacts on posting a link to his twitter
account. I've CC'ed him now. Maybe that works better.

Thanks,

tglx