linux-kernel - Re: [PATCH 2/4] x86: get rid of KERNEL_STACK

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Message-ID: <20150226114252.GA4593@gmail.com>
Date:	Thu, 26 Feb 2015 12:42:52 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 2/4] x86: get rid of KERNEL_STACK_OFFSET


* Andy Lutomirski <luto@...capital.net> wrote:

> >> I added that in and applied this patch.
> >
> > So this is not just slightly buggy, it's fundamentally 
> > wrong as well as it removes the possibility of an RSP 
> > value optimization from the 64-bit path, see my 
> > previous mail.
> 
> This is just trying to check that the function is 
> executing on the per-thread stack.  It was correct (and 
> fairly heavily tested by Tony) wither KERNEL_STACK_OFFSET 
> being nonzero, but we're checking the wrong page if 
> KERNEL_STACK_OFFSET becomes zero.
> 
> I don't think I understand your objection to this bit.

I object to the KERNEL_STACK_OFFSET removal patch you fixed 
here, not to the add-on fix in particular (which is correct 
in the context of that patch).

Thanks,

	Ingo
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