Re: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR

Kirill A. Shutemov
2022-06-29T00:53:45Z

On Tue, Jun 28, 2022 at 04:42:40PM -0700, Andy Lutomirski wrote:
> On 6/10/22 07:35, Kirill A. Shutemov wrote:
>
> > + /* Update CR3 to get LAM active */
> > + switch_mm(current->mm, current->mm, current);
>
> Can you at least justify this oddity? When changing an LDT, we use a
> dedicated mechanism. Is there a significant benefit to abusing switch_mm
> for this?

I'm not sure I follow. LAM mode is set in CR3. switch_mm() has to handle
it anyway to context switch. Why do you consider it abuse?

>
> Also, why can't we enable LAM on a multithreaded process? We can change an
> LDT, and the code isn't even particularly complicated.

I reworked this in v4[1] and it allows multithreaded processes. Have you
got that version?

Intel had issue with mail server, but I assumed it didn't affect my
patchset since I see it in the archive.

[1] https://lore.kernel.org/all/20220622162230.83474-1-kirill.shutemov@linux.intel.com/

--
Kirill A. Shutemov