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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 8980CC00307 for ; Fri, 6 Sep 2019 15:23:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6A24A214DE for ; Fri, 6 Sep 2019 15:23:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394798AbfIFPXV (ORCPT ); Fri, 6 Sep 2019 11:23:21 -0400 Received: from foss.arm.com ([217.140.110.172]:58296 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726019AbfIFPXU (ORCPT ); Fri, 6 Sep 2019 11:23:20 -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 AF61828; Fri, 6 Sep 2019 08:23:19 -0700 (PDT) Received: from [10.1.196.105] (unknown [10.1.196.105]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C6D063F59C; Fri, 6 Sep 2019 08:23:16 -0700 (PDT) Subject: Re: [PATCH v3 12/17] arm64, trans_pgd: complete generalization of trans_pgds To: Pavel Tatashin References: <20190821183204.23576-1-pasha.tatashin@soleen.com> <20190821183204.23576-13-pasha.tatashin@soleen.com> From: James Morse Cc: jmorris@namei.org, sashal@kernel.org, ebiederm@xmission.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, corbet@lwn.net, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, marc.zyngier@arm.com, vladimir.murzin@arm.com, matthias.bgg@gmail.com, bhsharma@redhat.com, linux-mm@kvack.org, mark.rutland@arm.com Message-ID: Date: Fri, 6 Sep 2019 16:23:15 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190821183204.23576-13-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Pavel, On 21/08/2019 19:31, Pavel Tatashin wrote: > Make the last private functions in page table copy path generlized for use > outside of hibernate. > > Switch to use the provided allocator, flags, and source page table. Also, > unify all copy function implementations to reduce the possibility of bugs. By changing it? No one has reported any problems. We're more likely to break it making unnecessary changes. Why is this necessary? > All page table levels are implemented symmetrically. > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c > index efd42509d069..ccd9900f8edb 100644 > --- a/arch/arm64/mm/trans_pgd.c > +++ b/arch/arm64/mm/trans_pgd.c > @@ -27,139 +27,157 @@ static void *trans_alloc(struct trans_pgd_info *info) > -static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr) > +static int copy_pte(struct trans_pgd_info *info, pte_t *dst_ptep, > + pte_t *src_ptep, unsigned long start, unsigned long end) > { > - pte_t pte = READ_ONCE(*src_ptep); > - > - if (pte_valid(pte)) { > - /* > - * Resume will overwrite areas that may be marked > - * read only (code, rodata). Clear the RDONLY bit from > - * the temporary mappings we use during restore. > - */ > - set_pte(dst_ptep, pte_mkwrite(pte)); > - } else if (debug_pagealloc_enabled() && !pte_none(pte)) { > - /* > - * debug_pagealloc will removed the PTE_VALID bit if > - * the page isn't in use by the resume kernel. It may have > - * been in use by the original kernel, in which case we need > - * to put it back in our copy to do the restore. > - * > - * Before marking this entry valid, check the pfn should > - * be mapped. > - */ > - BUG_ON(!pfn_valid(pte_pfn(pte))); > - > - set_pte(dst_ptep, pte_mkpresent(pte_mkwrite(pte))); > - } > -} > -static int copy_pte(pmd_t *dst_pmdp, pmd_t *src_pmdp, unsigned long start, > - unsigned long end) > -{ > - pte_t *src_ptep; > - pte_t *dst_ptep; > unsigned long addr = start; > + int i = pte_index(addr); > > - dst_ptep = (pte_t *)get_safe_page(GFP_ATOMIC); > - if (!dst_ptep) > - return -ENOMEM; > - pmd_populate_kernel(&init_mm, dst_pmdp, dst_ptep); > - dst_ptep = pte_offset_kernel(dst_pmdp, start); > - > - src_ptep = pte_offset_kernel(src_pmdp, start); > do { > - _copy_pte(dst_ptep, src_ptep, addr); > - } while (dst_ptep++, src_ptep++, addr += PAGE_SIZE, addr != end); > + pte_t src_pte = READ_ONCE(src_ptep[i]); > + > + if (pte_none(src_pte)) > + continue; > + if (info->trans_flags & TRANS_MKWRITE) > + src_pte = pte_mkwrite(src_pte); This should be unconditional. The purpose of this thing is to create a set of page tables you can use to overwrite all of memory. Why would you want to keep the RDONLY flag for normal memory? > + if (info->trans_flags & TRANS_MKVALID) > + src_pte = pte_mkpresent(src_pte); > + if (info->trans_flags & TRANS_CHECKPFN) { > + if (!pfn_valid(pte_pfn(src_pte))) > + return -ENXIO; > + } This lets you skip the pfn_valid() check if you want to create bogus mappings. This should not be conditional. This removes the BUG_ON(), which is there to make sure we stop if we find page-table corruption. Please keep the shape of _copy_pte() as it is. Putting a different mapping in the copied tables is risky, the code that does it should all be in one place, along with the justification of why its doing this. Anything else is harder to debug when it goes wrong. > + set_pte(&dst_ptep[i], src_pte); > + } while (addr += PAGE_SIZE, i++, addr != end && i < PTRS_PER_PTE); Incrementing pte/pud/pmg/pgd pointers is a common pattern in the kernel's page table walkers. Why do we need to change this to index it like an array? This needs to look like walk_page_range() as the eventual aim is to remove it, and use the core-code page table walker. (at the time it was merged the core-code page table walker removed block mappings it didn't like, which didn't go well.) This is a backwards step as it makes any attempt to remove this arch-specific walker harder. > > return 0; > } Thanks, James