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Date: Tue, 21 Jun 2016 10:16:46 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>, "the arch/x86 maintainers" <x86@...nel.org>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, 
	Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, 
	Brian Gerst <brgerst@...il.com>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Josh Poimboeuf <jpoimboe@...hat.com>, 
	Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

On Tue, Jun 21, 2016 at 9:45 AM, Andy Lutomirski <luto@...capital.net> wrote:
>
> So I'm leaning toward fewer cache entries per cpu, maybe just one.
> I'm all for making it a bit faster, but I think we should weigh that
> against increasing memory usage too much and thus scaring away the
> embedded folks.

I don't think the embedded folks will be scared by a per-cpu cache, if
it's just one or two entries.  And I really do think that even just
one or two entries will indeed catch a lot of the cases.

And yes, fork+execve() is too damn expensive in page table build-up
and tear-down. I'm not sure why bash doesn't do vfork+exec for when it
has to wait for the process anyway, but it doesn't seem to do that.

                 Linus

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