Question about switch_mm function

From: Valdis.Kletnieks@vt.edu (Valdis.Kletnieks at vt.edu)
To: kernelnewbies@lists.kernelnewbies.org
Subject: Question about switch_mm function
Date: Wed, 25 Mar 2015 13:25:04 -0400	[thread overview]
Message-ID: <6084.1427304304@turing-police.cc.vt.edu> (raw)
In-Reply-To: Your message of "Wed, 25 Mar 2015 21:35:22 +0530." <CAEDT3uTOUtS6jfpDQ+jpw-WABPBSk7f-nWEVQ5Eyaq=63o+7cg@mail.gmail.com>

On Wed, 25 Mar 2015 21:35:22 +0530, Sreejith M M said:

> > This code is handling context switch from a kernel thread back to user mode
> > thread so TLB entries are invalid translation for user mode thread and do
> > not correspond to user process pgd. It is Master kernel page table
> > translation as a result of kernel thread execution.
> >
> > -Rajat
> Hi Rajat,
>
> If that is the case, why this code is put under CONFIG_SMP switch?

Vastly simplified because I'm lazy :)

If you look at the code, it's poking the status on *other* CPUs.  That's why
the cpumask() stuff.

If you're on a single execution unit, you don't have to tell the other
CPU about the change in state, because there isn't an other CPU.
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