From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Andr=E9_Hentschel?= Subject: Re: [PATCH v6] arm: Preserve the user r/w register TPIDRURW on context, switch and fork Date: Tue, 18 Jun 2013 20:58:27 +0200 Message-ID: <51C0ADD3.7030102@dawncrow.de> References: <51BF8A1C.5070403@dawncrow.de> <20130618100715.GA3539@mudshark.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from moutng.kundenserver.de ([212.227.17.8]:54601 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756314Ab3FRS6f (ORCPT ); Tue, 18 Jun 2013 14:58:35 -0400 In-Reply-To: <20130618100715.GA3539@mudshark.cambridge.arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Will Deacon Cc: "linux-arch@vger.kernel.org" , Russell King - ARM Linux , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "gregkh@linuxfoundation.org" , Jonathan Austin On 18.06.2013 12:07, Will Deacon wrote: > On Mon, Jun 17, 2013 at 11:13:48PM +0100, Andr=E9 Hentschel wrote: >> From: Andr=E9 Hentschel >> >> Since commit 6a1c53124aa1 the user writeable TLS register was zeroed= to >> prevent it from being used as a covert channel between two tasks. >> >> There are more and more applications coming to Windows RT, >> Wine could support them, but mostly they expect to have >> the thread environment block (TEB) in TPIDRURW. >> >> This patch preserves that register per thread instead of clearing it= =2E >> Unlike the TPIDRURO, which is already switched, the TPIDRURW >> can be updated from userspace so needs careful treatment in the case= that we >> modify TPIDRURW and call fork(). To avoid this we must always read >> TPIDRURW in copy_thread. >> >> Signed-off-by: Andr=E9 Hentschel >> Signed-off-by: Will Deacon >> Signed-off-by: Jonathan Austin =20 >> >> --- >> This patch is against Linux 3.10-rc6 (7d132055814ef17a6c7b69f342244c= 410a5e000f) >> >> v2: rework and fixup of v1, based on a suggested patch by Will Deaco= n >> v3: total rework and fixup of v2 >> v4: removed condition on assembler instruction, >> adapted my code to kernel-style, both based on comments by Will = Deacon >> v5: rebased v4 on 3.10-rc2 and adding this version history >> v6: moved loading the TLS registers to the macros >> (fixing the "LDRD is not supported on all the CPUs we have" prob= lem) >=20 > You've changed quite a lot with this version, including the way the m= acro > parameters are passed. Why not just replace the problematic ldrd with= two > ldr instructions and be done with it? I don't think the simple build = error > warrants an overhaul of the code we already had. Wantig that patch to be in 3.11 i thought i should do more now to push = it. I'm still not that familiar with the process, but i think Russell King = would have done this easy change himself when he would be happy with it. =46urther this patch seems cleaner and much likely performing better. I'm off till saturday, hopefully i'm enlighted by feedback till then :) (just to be clear: i'm also happy with replacing ldrd with two ldr inst= ructions)