Re: [RFCv2 07/10] x86/mm: Handle tagged memory accesses from kernel threads

Peter Zijlstra
2022-05-11T07:23:26Z

On Wed, May 11, 2022 at 05:27:48AM +0300, Kirill A. Shutemov wrote:
> When a kernel thread performs memory access on behalf of a process (like
> in async I/O, io_uring, etc.) it has to respect tagging setup of the
> process as user addresses can include tags.
>
> Normally, LAM setup is per-thread and recorded in thread features, but
> for this use case kernel also tracks LAM setup per-mm. mm->context.lam
> would record LAM that allows the most tag bits among the threads of
> the mm.

Then why does it *ever* make sense to track it per thread? It's not like
it makes heaps of sense to allow one thread in a process to use LAM but
not the others.