Date: Thu, 26 Feb 2015 12:42:52 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>, X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Tony Luck <tony.luck@intel.com>
Subject: Re: [PATCH 2/4] x86: get rid of KERNEL_STACK_OFFSET
Message-ID: <20150226114252.GA4593@gmail.com>
References: <1424803895-4420-1-git-send-email-dvlasenk@redhat.com>
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 <CALCETrV-8JYofFAAzQmzDvm-p9VjBN_miAf9PR7CSTnid8UYNg@mail.gmail.com>
 <20150225094550.GB6676@gmail.com>
 <CALCETrUvoRUGS9O0baofq-HG-RWpfRXbw3YsEmTX7jSruVFU7Q@mail.gmail.com>
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* Andy Lutomirski <luto@amacapital.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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