From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AD48C4363A for ; Thu, 8 Oct 2020 10:45:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9815F2184D for ; Thu, 8 Oct 2020 10:45:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9815F2184D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AB4726B0062; Thu, 8 Oct 2020 06:45:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A63096B0068; Thu, 8 Oct 2020 06:45:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 92A636B006C; Thu, 8 Oct 2020 06:45:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0172.hostedemail.com [216.40.44.172]) by kanga.kvack.org (Postfix) with ESMTP id 62C866B0062 for ; Thu, 8 Oct 2020 06:45:13 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id E0974180AD804 for ; Thu, 8 Oct 2020 10:45:12 +0000 (UTC) X-FDA: 77348426064.15.iron35_421664b271d7 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id B58CC1814B0C7 for ; Thu, 8 Oct 2020 10:45:12 +0000 (UTC) X-HE-Tag: iron35_421664b271d7 X-Filterd-Recvd-Size: 5514 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Thu, 8 Oct 2020 10:45:12 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 21CCBD6E; Thu, 8 Oct 2020 03:45:11 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.52.79]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EBF83F70D; Thu, 8 Oct 2020 03:45:03 -0700 (PDT) Date: Thu, 8 Oct 2020 11:45:01 +0100 From: Mark Rutland To: Marco Elver Cc: Alexander Potapenko , Will Deacon , Andrew Morton , "H. Peter Anvin" , "Paul E. McKenney" , Andrey Konovalov , Andrey Ryabinin , Andy Lutomirski , Borislav Petkov , Catalin Marinas , Christoph Lameter , Dave Hansen , David Rientjes , Dmitriy Vyukov , Eric Dumazet , Greg Kroah-Hartman , Hillf Danton , Ingo Molnar , Jann Horn , Jonathan Cameron , Jonathan Corbet , Joonsoo Kim , Kees Cook , Pekka Enberg , Peter Zijlstra , SeongJae Park , Thomas Gleixner , Vlastimil Babka , the arch/x86 maintainers , "open list:DOCUMENTATION" , LKML , kasan-dev , Linux ARM , Linux Memory Management List Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64 Message-ID: <20201008104501.GB72325@C02TD0UTHF1T.local> References: <20200921132611.1700350-1-elver@google.com> <20200921132611.1700350-4-elver@google.com> <20200921143059.GO2139@willie-the-truck> <20200929140226.GB53442@C02TD0UTHF1T.local> <20201001175716.GA89689@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Oct 08, 2020 at 11:40:52AM +0200, Marco Elver wrote: > On Thu, 1 Oct 2020 at 19:58, Mark Rutland wrote: > [...] > > > > If you need virt_to_page() to work, the address has to be part of the > > > > linear/direct map. > [...] > > > > What's the underlying requirement here? Is this a performance concern, > > codegen/codesize, or something else? > > It used to be performance, since is_kfence_address() is used in the > fast path. However, with some further tweaks we just did to > is_kfence_address(), our benchmarks show a pointer load can be > tolerated. Great! I reckon that this is something we can optimize in futue if necessary (e.g. with some form of code-patching for immediate values), but it's good to have a starting point that works everywhere! [...] > > I'm not too worried about allocating this dynamically, but: > > > > * The arch code needs to set up the translation tables for this, as we > > cannot safely change the mapping granularity live. > > > > * As above I'm fairly certain x86 needs to use a carevout from the > > linear map to function correctly anyhow, so we should follow the same > > approach for both arm64 and x86. That might be a static carevout that > > we figure out the aliasing for, or something entirely dynamic. > > We're going with dynamically allocating the pool (for both x86 and > arm64), since any benefits we used to measure from the static pool are > no longer measurable (after removing a branch from > is_kfence_address()). It should hopefully simplify a lot of things, > given all the caveats that you pointed out. > > For arm64, the only thing left then is to fix up the case if the > linear map is not forced to page granularity. The simplest way to do this is to modify arm64's arch_add_memory() to force the entire linear map to be mapped at page granularity when KFENCE is enabled, something like: | diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c | index 936c4762dadff..f6eba0642a4a3 100644 | --- a/arch/arm64/mm/mmu.c | +++ b/arch/arm64/mm/mmu.c | @@ -1454,7 +1454,8 @@ int arch_add_memory(int nid, u64 start, u64 size, | { | int ret, flags = 0; | | - if (rodata_full || debug_pagealloc_enabled()) | + if (rodata_full || debug_pagealloc_enabled() || | + IS_ENABLED(CONFIG_KFENCE)) | flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; | | __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start), ... and I given that RODATA_FULL_DEFAULT_ENABLED is the default, I suspect it's not worth trying to only for that for the KFENCE region unless someone complains. Thanks, Mark.