linux-kernel - Re: [GIT PULL] x86 fixes

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Message-ID: <20100116205342.GA5725@lenovo>
Date:	Sat, 16 Jan 2010 23:53:42 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86 fixes

On Sat, Jan 16, 2010 at 12:34:42PM -0800, Linus Torvalds wrote:
> 
> 
> On Sat, 16 Jan 2010, Ingo Molnar wrote:
> > 
> > Cyrill Gorcunov (1):
> >       x86: kernel_thread() -- initialize SS to a known state
> 
> This looks bogus. Why does it do it only on x86-64?
> 
> Either people care about SS or they don't (the answer, I suspect, is "they 
> don't"). But if they care, we should do it on both 32-bit _and_ 64-bit, 
> no?
> 
> 		Linus

Linus, this is Xen specific. There was a Xen related series sent by Ian,
and seems we still need this patch together with get_kernel_rpl() (as I understand,
I'm not familiar with Xen code, that was a suspicious about SS as it's said
in commit message). So Ian mentioned

|
| > Yeah, I didn't found any explicit %ss reloading for this _particular_
| > case (as I marked in patch changelog). So the only suspicious is Xen
| > itself. So as only Christian get ability to test -- we will see the
| > results.
|
| The difference with Xen is that it must squash the RPL of SS (to 3 for
| 64 bit and 1 for 32 bit, 32 bit doesn't matter here though). Perhaps a
| NULL selector can only have RPL==0? (I'm away from my architecture docs
| so I can't check). In any case specifying a non-NULL SS selector allows
| the squashing to occur correctly.
|

In turn reported said that only _this_ patch alone doesn't help him and
Ian replied we need both patches.

Ian CC'ed if details needed.

	-- Cyrill
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