linux-kernel - Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd

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Message-ID: <20150612072302.GA7509@gmail.com>
Date:	Fri, 12 Jun 2015 09:23:02 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mml@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from
 the Xen guest code


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, Jun 11, 2015 at 1:37 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > Don't use "for_each_process_thread(g, p)". You only care about each mm, and 
> > threads all share the same mm, so just do
> >
> >     for_each_process(p)
> >
> > instead of iterating over all threads too.
> 
> Hmm. I may be wrong. It strikes me that one of the group leaders might have 
> exited but the subthreads live on. We'd see p->mm being NULL, even though the mm 
> was originally in use.
> 
> Ugh. So maybe the code really does need to iterate over all threads.

Yeah, for_each_process() is indeed no guarantee that we iterate over all mm's.

We might make it so: but that would mean restricting certain clone_flags variants 
- not sure that's possible with our current ABI usage?

Thanks,

	Ingo
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