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 D26CFC41604 for ; Tue, 6 Oct 2020 06:29:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8EC0720796 for ; Tue, 6 Oct 2020 06:29:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727048AbgJFG31 (ORCPT ); Tue, 6 Oct 2020 02:29:27 -0400 Received: from foss.arm.com ([217.140.110.172]:39454 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726022AbgJFG31 (ORCPT ); Tue, 6 Oct 2020 02:29:27 -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 3C9B71435; Mon, 5 Oct 2020 23:29:26 -0700 (PDT) Received: from [10.163.74.99] (unknown [10.163.74.99]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B50FF3F66B; Mon, 5 Oct 2020 23:29:22 -0700 (PDT) Subject: Re: [PATCH] arm64/mm: Validate hotplug range before creating linear mapping To: Ard Biesheuvel Cc: Will Deacon , Linux ARM , Catalin Marinas , Mark Rutland , Steven Price , Robin Murphy , David Hildenbrand , Andrew Morton , Linux Kernel Mailing List References: <1600332402-30123-1-git-send-email-anshuman.khandual@arm.com> <20200928203539.GA12218@willie-the-truck> <09266aed-7eef-5b16-5d52-0dcb7dcb7246@arm.com> <20200929152221.GA13995@willie-the-truck> From: Anshuman Khandual Message-ID: <0784f1ec-c044-7fc8-70dc-a378c2b586fa@arm.com> Date: Tue, 6 Oct 2020 11:58:51 +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: 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 09/30/2020 04:31 PM, Ard Biesheuvel wrote: > On Wed, 30 Sep 2020 at 10:03, Anshuman Khandual > wrote: >> >> >> On 09/29/2020 08:52 PM, Will Deacon wrote: >>> On Tue, Sep 29, 2020 at 01:34:24PM +0530, Anshuman Khandual wrote: >>>> >>>> >>>> On 09/29/2020 02:05 AM, Will Deacon wrote: >>>>> On Thu, Sep 17, 2020 at 02:16:42PM +0530, 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))); >>>>>> +} >>>>> >>>>> Why isn't this implemented using the existing __is_lm_address()? >>>> >>>> Not sure, if I understood your suggestion here. The physical address range >>>> [start..start + size] needs to be checked against maximum physical range >>>> that can be represented inside effective boundaries for the linear mapping >>>> i.e [__pa(_PAGE_OFFSET(vabits_actual)..__pa(PAGE_END - 1)]. >>>> >>>> Are you suggesting [start..start + size] should be first be converted into >>>> a virtual address range and then checked against __is_lm_addresses() ? But >>>> is not deriving the physical range from from know limits of linear mapping >>>> much cleaner ? >>> >>> I just think having a function called "inside_linear_region()" as well as a >>> macro called "__is_lm_address()" is weird when they have completely separate >>> implementations. They're obviously trying to do the same thing, just the >>> first one gets given physical address as parameters. >>> >>> Implementing one in terms of the other is much better for maintenance. >> >> /* >> * The linear kernel range starts at the bottom of the virtual address >> * space. Testing the top bit for the start of the region is a >> * sufficient check and avoids having to worry about the tag. >> */ >> #define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1))) >> >> __is_lm_address() currently just check the highest bit in a virtual address >> where the linear mapping ends i.e the lower half and all other kernel mapping >> starts i.e the upper half. But I would believe, it misses the blind range >> [_PAGE_OFFSET(VA_BITS).._PAGE_OFFSET(vabits_actual)] in some configurations, >> even though it does not really affect anything because it gets ignored by the >> MMU. Hence in current form __is_lm_address() cannot be used to derive maximum >> linear range and it's corresponding physical range for hotplug range check. >> > > This is actually something that I brought up when the 52-bit VA > changes were under review: currently, we split the VA space in half, > and use the lower half for the linear range, and the upper half for > vmalloc, kernel, modules, vmemmap etc Right. > > When we run a 48-bit kernel on 52-bit capable hardware, we mostly > stick with the same arrangement: 2^51 bytes of linear range, but only > 2^47 bytes of vmalloc range (as the size is fixed), and so we are > wasting 15/16 of the vmalloc region (2^51 - 2^47), by not using it to > map anything. Right, there are unused gaps in the kernel virtual space with current arrangement for various sections. > > So it would be better to get away from this notion that the VA space > is divided evenly between linear and vmalloc regions, and use the > entire range between ~0 << 52 and ~0 << 47 for the linear region (Note > that the KASAN region defimnition will overlap the linear region in > this case, by we should be able to sort that at runtime) Right, kernel virtual space management needs rethink for optimal address range utilization while reducing unused areas. I have been experimenting with this for a while but nothing particular to propose yet. Nonetheless for now, we need to fix this address range problem for memory hotplug.