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=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 AABCCC433E0 for ; Tue, 16 Jun 2020 10:59:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 891BD20A8B for ; Tue, 16 Jun 2020 10:59:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728416AbgFPK7c (ORCPT ); Tue, 16 Jun 2020 06:59:32 -0400 Received: from foss.arm.com ([217.140.110.172]:35430 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728306AbgFPK7Z (ORCPT ); Tue, 16 Jun 2020 06:59:25 -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 D2B221F1; Tue, 16 Jun 2020 03:59:24 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.1.157]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 401933F6CF; Tue, 16 Jun 2020 03:59:23 -0700 (PDT) Date: Tue, 16 Jun 2020 11:59:20 +0100 From: Mark Rutland To: Andrei Vagin Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Vincenzo Frascino , Thomas Gleixner , Dmitry Safonov Subject: Re: [PATCH 1/6] arm64/vdso: use the fault callback to map vvar pages Message-ID: <20200616105920.GB11780@C02TD0UTHF1T.local> References: <20200616075545.312684-1-avagin@gmail.com> <20200616075545.312684-2-avagin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200616075545.312684-2-avagin@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 16, 2020 at 12:55:40AM -0700, Andrei Vagin wrote: > This is required to support time namespaces where a time namespace data > page is different for each namespace. Can you please give a bit more of an introduction to the changes here? As-is, this doesn't give reviewers the necessary context to understand the change, nor does it justify it. Ideally, a commit message for this should look something like: | Currently the vdso has no awareness of time namespaces, which may | apply distinct offsets to processes in different namespaces. To handle | this within the vdso, we'll need to expose a per-namespace data page. | | As a preparatory step, this patch separates the vdso data page from | the code pages, and has it faulted in via its own fault callback. | Subsquent patches will extend this to support distinct pages per time | namespace. Otherwise, I have a few minor comments below. > Reviewed-by: Vincenzo Frascino > Reviewed-by: Dmitry Safonov > Signed-off-by: Andrei Vagin > --- > arch/arm64/kernel/vdso.c | 24 +++++++++++++++--------- > 1 file changed, 15 insertions(+), 9 deletions(-) > > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > index 4e016574bd91..b0aec4e8c9b4 100644 > --- a/arch/arm64/kernel/vdso.c > +++ b/arch/arm64/kernel/vdso.c > @@ -108,28 +108,32 @@ static int __vdso_init(enum vdso_abi abi) > PAGE_SHIFT; > > /* Allocate the vDSO pagelist, plus a page for the data. */ > - vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages + 1, > + vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages, > sizeof(struct page *), > GFP_KERNEL); The comment above is now stale. Can you please update it, or (event better) delete it entirely? > if (vdso_pagelist == NULL) > return -ENOMEM; > > - /* Grab the vDSO data page. */ > - vdso_pagelist[0] = phys_to_page(__pa_symbol(vdso_data)); > - > - > /* Grab the vDSO code pages. */ > pfn = sym_to_pfn(vdso_info[abi].vdso_code_start); > > for (i = 0; i < vdso_info[abi].vdso_pages; i++) > - vdso_pagelist[i + 1] = pfn_to_page(pfn + i); > + vdso_pagelist[i] = pfn_to_page(pfn + i); > > - vdso_info[abi].dm->pages = &vdso_pagelist[0]; > - vdso_info[abi].cm->pages = &vdso_pagelist[1]; > + vdso_info[abi].cm->pages = vdso_pagelist; > > return 0; > } > > +static vm_fault_t vvar_fault(const struct vm_special_mapping *sm, > + struct vm_area_struct *vma, struct vm_fault *vmf) > +{ > + if (vmf->pgoff == 0) > + return vmf_insert_pfn(vma, vmf->address, > + sym_to_pfn(vdso_data)); > + return VM_FAULT_SIGBUS; > +} This might look better as: | if (vmf->pgoff != 0) | return VM_FAULT_SIGBUS; | | return vmf_insert_pfn(vma, vmf->address, sym_to_pfn(vdso_data)); > + > static int __setup_additional_pages(enum vdso_abi abi, > struct mm_struct *mm, > struct linux_binprm *bprm, > @@ -150,7 +154,7 @@ static int __setup_additional_pages(enum vdso_abi abi, > } > > ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE, > - VM_READ|VM_MAYREAD, > + VM_READ|VM_MAYREAD|VM_PFNMAP, This change needs to be explained in the commit message. WHy is it necessary, and why only so for the data page? Thanks, Mark. > vdso_info[abi].dm); > if (IS_ERR(ret)) > goto up_fail; > @@ -209,6 +213,7 @@ static struct vm_special_mapping aarch32_vdso_maps[] = { > #ifdef CONFIG_COMPAT_VDSO > [AA32_MAP_VVAR] = { > .name = "[vvar]", > + .fault = vvar_fault, > }, > [AA32_MAP_VDSO] = { > .name = "[vdso]", > @@ -376,6 +381,7 @@ enum aarch64_map { > static struct vm_special_mapping aarch64_vdso_maps[] __ro_after_init = { > [AA64_MAP_VVAR] = { > .name = "[vvar]", > + .fault = vvar_fault, > }, > [AA64_MAP_VDSO] = { > .name = "[vdso]", > -- > 2.24.1 >