linux-kernel - Re: [PATCHv2] arm: Preserve TPIDRURW on context switch

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Date:	Mon, 22 Apr 2013 23:07:35 +0200
From:	André Hentschel <nerv@...ncrow.de>
To:	Will Deacon <will.deacon@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: [PATCHv2] arm: Preserve TPIDRURW on context switch

Am 22.04.2013 17:18, schrieb Will Deacon:
> On Mon, Apr 22, 2013 at 03:36:16PM +0100, Russell King - ARM Linux wrote:
>> On Fri, Apr 19, 2013 at 05:54:35PM +0200, André Hentschel wrote:
>>> From: =?UTF-8?q?Andr=C3=A9=20Hentschel?= <nerv@...ncrow.de>
>>>
>>> There are more and more applications coming to WinRT, Wine could support them,
>>> but mostly they expect to have the thread environment block (TEB) in TPIDRURW.
>>> This register must be preserved per thread instead of being cleared.
>>>
>>> Signed-off-by: André Hentschel <nerv@...ncrow.de>
>>
>> This actually makes things less efficient all round, because you
>> now use the value immediately after loading, which means it will cause
>> pipeline stalls, certainly on older CPUs.
>>
>> Could you please rework the patch to try avoiding soo many modifications
>> to the way things have been done here?
> 
> copy_thread also needs updating so that the *register* value for the parent
> is copied to the child, since the parent may have written the register
> after the last context-switch, meaning that tp_value is out-of-date.

Thank you both for reviewing.

I guess you mostly mean "ldr	r6, [r2, #TI_CPU_DOMAIN]".
I just thought about old CPUs and remembered again that we at Wine
need that patch only on v7 (and later). So is it ok to introduce a set_tls_v7
in tls.h and make use of CONFIG_CPU_V7 compile-time check in
the changed files and in the copy_thread function?
Do i need any further flag checks in copy_thread or can i use the
compile-time check to add unconditional code?

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