From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f43.google.com (mail-lf0-f43.google.com [209.85.215.43]) by kanga.kvack.org (Postfix) with ESMTP id A6A8D6B0038 for ; Fri, 27 Nov 2015 03:12:20 -0500 (EST) Received: by lffu14 with SMTP id u14so120857704lff.1 for ; Fri, 27 Nov 2015 00:12:19 -0800 (PST) Received: from relay.parallels.com (relay.parallels.com. [195.214.232.42]) by mx.google.com with ESMTPS id l20si20815556lfi.69.2015.11.27.00.12.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 27 Nov 2015 00:12:18 -0800 (PST) Subject: Re: [PATCH RFT] arm64: kasan: Make KASAN work with 16K pages + 48 bit VA References: <1448543686-31869-1-git-send-email-aryabinin@virtuozzo.com> From: Andrey Ryabinin Message-ID: <5658106C.10207@virtuozzo.com> Date: Fri, 27 Nov 2015 11:12:28 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ard Biesheuvel Cc: Catalin Marinas , Will Deacon , "linux-arm-kernel@lists.infradead.org" , Yury , Alexey Klimov , Arnd Bergmann , "linux-mm@kvack.org" , Linus Walleij , "linux-kernel@vger.kernel.org" , David Keitel , Alexander Potapenko , Dmitry Vyukov , "Suzuki K. Poulose" , Mark Rutland On 11/26/2015 07:40 PM, Ard Biesheuvel wrote: > On 26 November 2015 at 14:14, Andrey Ryabinin wrote: >> Currently kasan assumes that shadow memory covers one or more entire PGDs. >> That's not true for 16K pages + 48bit VA space, where PGDIR_SIZE is bigger >> than the whole shadow memory. >> >> This patch tries to fix that case. >> clear_page_tables() is a new replacement of clear_pgs(). Instead of always >> clearing pgds it clears top level page table entries that entirely belongs >> to shadow memory. >> In addition to 'tmp_pg_dir' we now have 'tmp_pud' which is used to store >> puds that now might be cleared by clear_page_tables. >> >> Reported-by: Suzuki K. Poulose >> Signed-off-by: Andrey Ryabinin > > I would argue that the Kasan code is complicated enough, and we should > avoid complicating it even further for a configuration that is highly > theoretical in nature. > > In a 16k configuration, the 4th level only adds a single bit of VA > space (which is, as I understand it, exactly the issue you need to > address here since the top level page table has only 2 entries and > hence does not divide by 8 cleanly), which means you are better off > using 3 levels unless you *really* need more than 128 TB of VA space. > > So can't we just live with the limitation, and keep the current code? No objections from my side. Let's keep the current code. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org