Re: [PATCH 06/10] mm,x86: skip cr4 and ldt reload when mm stays the same

[Andy Lutomirski]

On Sat, Jul 28, 2018 at 2:53 PM, Rik van Riel <riel@xxxxxxxxxxx> wrote:
> When switching back from lazy TLB mode to a thread of the same process
> that switched into lazy TLB mode, we still have the cr4 (and sometimes
> LDT) of that process loaded, and there is no need to reload it.
>
> When there was no TLB flush while the CPU was in lazy TLB mode, the
> current code in switch_mm_irqs_off already avoids the reload, by
> returning early.
>
> However, when the TLB contents on the CPU are out of date, and we
> flush the TLB for the task, we fall through to the regular context
> switching code. This patch teaches that code to skip the cr4 and LDT
> flushes when switching back to the same mm after a flush.

Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>