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Received: from shell.armlinux.org.uk ([2001:4d48:ad52:3201:5054:ff:fe00:4ec]:40240) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jZGfw-0000fU-St; Thu, 14 May 2020 17:25:37 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1jZGfv-0000hD-S4; Thu, 14 May 2020 17:25:35 +0100 Date: Thu, 14 May 2020 17:25:35 +0100 From: Russell King - ARM Linux admin To: Arnd Bergmann Subject: Re: ARM: static kernel in vmalloc space Message-ID: <20200514162535.GP1551@shell.armlinux.org.uk> References: <20200503145017.GA5074@afzalpc> <20200504091018.GA24897@afzalpc> <20200511142113.GA31707@afzalpc> <20200512104758.GA12980@afzalpc> <20200514111755.GA4997@afzalpc> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200514_092547_168873_D353F9BB X-CRM114-Status: GOOD ( 18.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: afzal mohammed , "linux-kernel@vger.kernel.org" , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, May 14, 2020 at 02:41:11PM +0200, Arnd Bergmann wrote: > On Thu, May 14, 2020 at 1:18 PM afzal mohammed wrote: > > On Tue, May 12, 2020 at 09:49:59PM +0200, Arnd Bergmann wrote: > > > > > Any idea which bit you want to try next? > > > > My plan has been to next post patches for the static kernel migration > > to vmalloc space (currently the code is rigid, taking easy route > > wherever possible & not of high quality) as that feature has an > > independent existence & adds value by itself. And then start working > > on other steps towards VMSPLIT_4G_4G. > > > > Now that you mentioned about other things, i will slowly start those > > as well. > > Sounds good. > > > > Creating a raw_copy_{from,to}_user() > > > based on get_user_pages()/kmap_atomic()/memcpy() is probably a good > > > next thing to do. I think it can be done one page at a time with only > > > checking for > > > get_fs(), access_ok(), and page permissions, while get_user()/put_user() > > > need to handle a few more corner cases. > > > > Before starting w/ other things, i would like to align on the high > > level design, > > > > My understanding (mostly based on your comments) as follows, > > (i currently do not have a firm grip over these things, hope to have > > it once started w/ the implementation) > > > > 1. SoC w/ LPAE > > 2. TTBR1 (top 256MB) for static kernel, modules, io mappings, vmalloc, > > kmap, fixmap & vectors > > Right, these kind of go together because pre-LPAE cannot do the > same TTBR1 split, and they more frequently have conflicting > static mappings. > > It's clearly possible to do something very similar for older chips > (v6 or v7 without LPAE, possibly even v5), it just gets harder > while providing less benefit. Forget about doing this for anything without a PIPT cache - or you're going to end up having to flush the data cache each time you enter or exit the kernel. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel