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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 51A1EC4363D for ; Wed, 7 Oct 2020 02:50:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20301207EA for ; Wed, 7 Oct 2020 02:50:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727071AbgJGCut (ORCPT ); Tue, 6 Oct 2020 22:50:49 -0400 Received: from foss.arm.com ([217.140.110.172]:34800 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726073AbgJGCut (ORCPT ); Tue, 6 Oct 2020 22:50:49 -0400 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 A0E85113E; Tue, 6 Oct 2020 19:50:48 -0700 (PDT) Received: from [192.168.0.130] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 68F343F71F; Tue, 6 Oct 2020 19:50:45 -0700 (PDT) Subject: Re: [PATCH] arm64/mm: Validate hotplug range before creating linear mapping To: David Hildenbrand , linux-arm-kernel@lists.infradead.org Cc: will@kernel.org, catalin.marinas@arm.com, Mark Rutland , Ard Biesheuvel , Steven Price , Robin Murphy , Andrew Morton , linux-kernel@vger.kernel.org, Michal Hocko References: <1600332402-30123-1-git-send-email-anshuman.khandual@arm.com> <7c39c046-b950-ea4c-fa4d-e0a5d6171147@redhat.com> From: Anshuman Khandual Message-ID: <72ea7056-5289-3eb0-eca9-a8444524667e@arm.com> Date: Wed, 7 Oct 2020 08:20:14 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <7c39c046-b950-ea4c-fa4d-e0a5d6171147@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/06/2020 09:04 PM, David Hildenbrand wrote: > On 17.09.20 10:46, Anshuman Khandual wrote: >> During memory hotplug process, the linear mapping should not be created for >> a given memory range if that would fall outside the maximum allowed linear >> range. Else it might cause memory corruption in the kernel virtual space. >> >> Maximum linear mapping region is [PAGE_OFFSET..(PAGE_END -1)] accommodating >> both its ends but excluding PAGE_END. Max physical range that can be mapped >> inside this linear mapping range, must also be derived from its end points. >> >> When CONFIG_ARM64_VA_BITS_52 is enabled, PAGE_OFFSET is computed with the >> assumption of 52 bits virtual address space. However, if the CPU does not >> support 52 bits, then it falls back using 48 bits instead and the PAGE_END >> is updated to reflect this using the vabits_actual. As for PAGE_OFFSET, >> bits [51..48] are ignored by the MMU and remain unchanged, even though the >> effective start address of linear map is now slightly different. Hence, to >> reliably check the physical address range mapped by the linear map, the >> start address should be calculated using vabits_actual. This ensures that >> arch_add_memory() validates memory hot add range for its potential linear >> mapping requirement, before creating it with __create_pgd_mapping(). >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Mark Rutland >> Cc: Ard Biesheuvel >> Cc: Steven Price >> Cc: Robin Murphy >> Cc: David Hildenbrand >> Cc: Andrew Morton >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Fixes: 4ab215061554 ("arm64: Add memory hotplug support") >> Signed-off-by: Anshuman Khandual >> --- >> arch/arm64/mm/mmu.c | 27 +++++++++++++++++++++++++++ >> 1 file changed, 27 insertions(+) >> >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index 75df62fea1b6..d59ffabb9c84 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -1433,11 +1433,38 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size) >> free_empty_tables(start, end, PAGE_OFFSET, PAGE_END); >> } >> >> +static bool inside_linear_region(u64 start, u64 size) >> +{ >> + /* >> + * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)] >> + * accommodating both its ends but excluding PAGE_END. Max physical >> + * range which can be mapped inside this linear mapping range, must >> + * also be derived from its end points. >> + * >> + * With CONFIG_ARM64_VA_BITS_52 enabled, PAGE_OFFSET is defined with >> + * the assumption of 52 bits virtual address space. However, if the >> + * CPU does not support 52 bits, it falls back using 48 bits and the >> + * PAGE_END is updated to reflect this using the vabits_actual. As >> + * for PAGE_OFFSET, bits [51..48] are ignored by the MMU and remain >> + * unchanged, even though the effective start address of linear map >> + * is now slightly different. Hence, to reliably check the physical >> + * address range mapped by the linear map, the start address should >> + * be calculated using vabits_actual. >> + */ >> + return ((start >= __pa(_PAGE_OFFSET(vabits_actual))) >> + && ((start + size) <= __pa(PAGE_END - 1))); >> +} >> + >> int arch_add_memory(int nid, u64 start, u64 size, >> struct mhp_params *params) >> { >> int ret, flags = 0; >> >> + if (!inside_linear_region(start, size)) { >> + pr_err("[%llx %llx] is outside linear mapping region\n", start, start + size); >> + return -EINVAL; >> + } >> + >> if (rodata_full || debug_pagealloc_enabled()) >> flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; >> >> > > Can we please provide a generic way to figure limits like that out, > especially, before calling add_memory() and friends? > > We do have __add_pages()->check_hotplug_memory_addressable() where we > already check against MAX_PHYSMEM_BITS. Initially, I thought about check_hotplug_memory_addressable() but the existing check that asserts end of hotplug wrt MAX_PHYSMEM_BITS, is generic in nature. AFAIK the linear mapping problem is arm64 specific, hence I was not sure whether to add an arch specific callback which will give platform an opportunity to weigh in for these ranges. But hold on, check_hotplug_memory_addressable() only gets called from __add_pages() after linear mapping creation in arch_add_memory(). How would it help ? We need some thing for add_memory(), its variants and also possibly for memremap_pages() when it calls arch_add_memory(). > > What I'd prefer is a way to get > > 1. Lower address limit we can use for add_memory() and friends > 2. Upper address limit we can use for add_memory() and friends A structure based range. > > something like > > > struct range memhp_get_addressable_range(void) > { > const u64 max_phys = (1ull << (MAX_PHYSMEM_BITS + 1)) - 1; > struct range range = arch_get_mappable_range(); What would you suggest as the default fallback range if a platform does not define this callback. > > if (range.start > max_phys) { > range.start = 0; > range.end = 0; > } > range.end = max_t(u64, range.end, max_phys); min_t instead ? > > return range; > } > > > That, we can use in check_hotplug_memory_addressable(), and also allow > add_memory*() users to make use of it. So this check would happen twice during a hotplug ?