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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 2959EC388F9 for ; Tue, 27 Oct 2020 08:49:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DAF832225C for ; Tue, 27 Oct 2020 08:49:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603788561; bh=vqvHVfwUem4JOBq/WXsfNE79L5Iz5nEhnMlkJj2ElFU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=d1pxneT4IJF5KDe9QqWFomCp71WkoqAiCHLtubTM2nKhtusXjIsgsulKq/3aiBvNb Mj9dBzEluyg2QU3cbpcbZbz+BsnK4yJ4n5ubNBIOyZ+lfQzpf2YU6+KfoFVM384INc SqOO/snPjtfD3BBLId4/clddpbP6fhuGFxxNHk/4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2509340AbgJ0ItT (ORCPT ); Tue, 27 Oct 2020 04:49:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:50878 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2509336AbgJ0ItR (ORCPT ); Tue, 27 Oct 2020 04:49:17 -0400 Received: from kernel.org (unknown [87.70.96.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 817B6207DE; Tue, 27 Oct 2020 08:49:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603788557; bh=vqvHVfwUem4JOBq/WXsfNE79L5Iz5nEhnMlkJj2ElFU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cob/039dcWnn8OjH5If0m1K0e5hz+wi7uaTqafHhMC0w6AKDJ7mof/L9QVAWjAi5m AzwVpAcX/G3bIeFGz/QZ6LDXFrWjC3A32wjsC/UaCx/T35y4jeNZtg1G5OqKcQamFp mFhuBk5Uhn3ItuoN/wmMtQFg0IPWtBPQaAK5nUZY= Date: Tue, 27 Oct 2020 10:49:02 +0200 From: Mike Rapoport To: "Edgecombe, Rick P" Cc: "david@redhat.com" , "cl@linux.com" , "gor@linux.ibm.com" , "hpa@zytor.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "borntraeger@de.ibm.com" , "penberg@kernel.org" , "linux-mm@kvack.org" , "iamjoonsoo.kim@lge.com" , "will@kernel.org" , "aou@eecs.berkeley.edu" , "kirill@shutemov.name" , "rientjes@google.com" , "rppt@linux.ibm.com" , "paulus@samba.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "pavel@ucw.cz" , "sparclinux@vger.kernel.org" , "akpm@linux-foundation.org" , "luto@kernel.org" , "davem@davemloft.net" , "mpe@ellerman.id.au" , "benh@kernel.crashing.org" , "linuxppc-dev@lists.ozlabs.org" , "rjw@rjwysocki.net" , "tglx@linutronix.de" , "linux-riscv@lists.infradead.org" , "x86@kernel.org" , "linux-pm@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "palmer@dabbelt.com" , "Brown, Len" , "mingo@redhat.com" , "linux-s390@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "paul.walmsley@sifive.com" Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Message-ID: <20201027084902.GH1154158@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> <20201025101555.3057-3-rppt@kernel.org> <20201026091554.GB1154158@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Mon, Oct 26, 2020 at 06:57:32PM +0000, Edgecombe, Rick P wrote: > On Mon, 2020-10-26 at 11:15 +0200, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 12:38:32AM +0000, Edgecombe, Rick P wrote: > > > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > > > From: Mike Rapoport > > > > > > > > When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page > > > > may > > > > be > > > > not present in the direct map and has to be explicitly mapped > > > > before > > > > it > > > > could be copied. > > > > > > > > On arm64 it is possible that a page would be removed from the > > > > direct > > > > map > > > > using set_direct_map_invalid_noflush() but __kernel_map_pages() > > > > will > > > > refuse > > > > to map this page back if DEBUG_PAGEALLOC is disabled. > > > > > > It looks to me that arm64 __kernel_map_pages() will still attempt > > > to > > > map it if rodata_full is true, how does this happen? > > > > Unless I misread the code, arm64 requires both rodata_full and > > debug_pagealloc_enabled() to be true for __kernel_map_pages() to do > > anything. > > But rodata_full condition applies to set_direct_map_*_noflush() as > > well, > > so with !rodata_full the linear map won't be ever changed. > > Hmm, looks to me that __kernel_map_pages() will only skip it if both > debug pagealloc and rodata_full are false. > > But now I'm wondering if maybe we could simplify things by just moving > the hibernate unmapped page logic off of the direct map. On x86, > text_poke() used to use this reserved fixmap pte thing that it could > rely on to remap memory with. If hibernate had some separate pte for > remapping like that, then we could not have any direct map restrictions > caused by it/kernel_map_pages(), and it wouldn't have to worry about > relying on anything else. Well, there is map_kernel_range() that can be used by hibernation as there is no requirement for particular virtual address, but that would be quite costly if done for every page. Maybe we can do somthing like if (kernel_page_present(s_page)) { do_copy_page(dst, page_address(s_page)); } else { map_kernel_range_noflush(page_address(page), PAGE_SIZE, PROT_READ, &page); do_copy_page(dst, page_address(s_page)); unmap_kernel_range_noflush(page_address(page), PAGE_SIZE); } But it seems that a prerequisite for changing the way a page is mapped in safe_copy_page() would be to teach hibernation that a mapping here may fail. -- Sincerely yours, Mike. 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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 2831CC4363A for ; Tue, 27 Oct 2020 08:49:43 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BBCA0207DE for ; Tue, 27 Oct 2020 08:49:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="cwQxOyJN"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cob/039d" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BBCA0207DE Authentication-Results: mail.kernel.org; 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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXKfZ-0004I8-9U; Tue, 27 Oct 2020 08:49:29 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXKfO-0004Dr-EY; Tue, 27 Oct 2020 08:49:19 +0000 Received: from kernel.org (unknown [87.70.96.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 817B6207DE; Tue, 27 Oct 2020 08:49:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603788557; bh=vqvHVfwUem4JOBq/WXsfNE79L5Iz5nEhnMlkJj2ElFU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cob/039dcWnn8OjH5If0m1K0e5hz+wi7uaTqafHhMC0w6AKDJ7mof/L9QVAWjAi5m AzwVpAcX/G3bIeFGz/QZ6LDXFrWjC3A32wjsC/UaCx/T35y4jeNZtg1G5OqKcQamFp mFhuBk5Uhn3ItuoN/wmMtQFg0IPWtBPQaAK5nUZY= Date: Tue, 27 Oct 2020 10:49:02 +0200 From: Mike Rapoport To: "Edgecombe, Rick P" Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Message-ID: <20201027084902.GH1154158@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> <20201025101555.3057-3-rppt@kernel.org> <20201026091554.GB1154158@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201027_044918_795560_03DEF45A X-CRM114-Status: GOOD ( 27.73 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "benh@kernel.crashing.org" , "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "paulus@samba.org" , "pavel@ucw.cz" , "hpa@zytor.com" , "sparclinux@vger.kernel.org" , "cl@linux.com" , "will@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "mpe@ellerman.id.au" , "x86@kernel.org" , "rppt@linux.ibm.com" , "borntraeger@de.ibm.com" , "mingo@redhat.com" , "rientjes@google.com" , "Brown, Len" , "aou@eecs.berkeley.edu" , "gor@linux.ibm.com" , "linux-pm@vger.kernel.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "tglx@linutronix.de" , "iamjoonsoo.kim@lge.com" , "linux-arm-kernel@lists.infradead.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , "palmer@dabbelt.com" , "akpm@linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , "davem@davemloft.net" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Mon, Oct 26, 2020 at 06:57:32PM +0000, Edgecombe, Rick P wrote: > On Mon, 2020-10-26 at 11:15 +0200, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 12:38:32AM +0000, Edgecombe, Rick P wrote: > > > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > > > From: Mike Rapoport > > > > > > > > When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page > > > > may > > > > be > > > > not present in the direct map and has to be explicitly mapped > > > > before > > > > it > > > > could be copied. > > > > > > > > On arm64 it is possible that a page would be removed from the > > > > direct > > > > map > > > > using set_direct_map_invalid_noflush() but __kernel_map_pages() > > > > will > > > > refuse > > > > to map this page back if DEBUG_PAGEALLOC is disabled. > > > > > > It looks to me that arm64 __kernel_map_pages() will still attempt > > > to > > > map it if rodata_full is true, how does this happen? > > > > Unless I misread the code, arm64 requires both rodata_full and > > debug_pagealloc_enabled() to be true for __kernel_map_pages() to do > > anything. > > But rodata_full condition applies to set_direct_map_*_noflush() as > > well, > > so with !rodata_full the linear map won't be ever changed. > > Hmm, looks to me that __kernel_map_pages() will only skip it if both > debug pagealloc and rodata_full are false. > > But now I'm wondering if maybe we could simplify things by just moving > the hibernate unmapped page logic off of the direct map. On x86, > text_poke() used to use this reserved fixmap pte thing that it could > rely on to remap memory with. If hibernate had some separate pte for > remapping like that, then we could not have any direct map restrictions > caused by it/kernel_map_pages(), and it wouldn't have to worry about > relying on anything else. Well, there is map_kernel_range() that can be used by hibernation as there is no requirement for particular virtual address, but that would be quite costly if done for every page. Maybe we can do somthing like if (kernel_page_present(s_page)) { do_copy_page(dst, page_address(s_page)); } else { map_kernel_range_noflush(page_address(page), PAGE_SIZE, PROT_READ, &page); do_copy_page(dst, page_address(s_page)); unmap_kernel_range_noflush(page_address(page), PAGE_SIZE); } But it seems that a prerequisite for changing the way a page is mapped in safe_copy_page() would be to teach hibernation that a mapping here may fail. -- Sincerely yours, Mike. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv 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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 37E4DC4363A for ; Tue, 27 Oct 2020 08:51:27 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 62CA9207DE for ; Tue, 27 Oct 2020 08:51:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cob/039d" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 62CA9207DE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4CL5630X0QzDqQP for ; Tue, 27 Oct 2020 19:51:23 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=198.145.29.99; helo=mail.kernel.org; envelope-from=rppt@kernel.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=default header.b=cob/039d; dkim-atps=neutral Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4CL53h5C1zzDqJf for ; Tue, 27 Oct 2020 19:49:20 +1100 (AEDT) Received: from kernel.org (unknown [87.70.96.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 817B6207DE; Tue, 27 Oct 2020 08:49:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603788557; bh=vqvHVfwUem4JOBq/WXsfNE79L5Iz5nEhnMlkJj2ElFU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cob/039dcWnn8OjH5If0m1K0e5hz+wi7uaTqafHhMC0w6AKDJ7mof/L9QVAWjAi5m AzwVpAcX/G3bIeFGz/QZ6LDXFrWjC3A32wjsC/UaCx/T35y4jeNZtg1G5OqKcQamFp mFhuBk5Uhn3ItuoN/wmMtQFg0IPWtBPQaAK5nUZY= Date: Tue, 27 Oct 2020 10:49:02 +0200 From: Mike Rapoport To: "Edgecombe, Rick P" Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Message-ID: <20201027084902.GH1154158@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> <20201025101555.3057-3-rppt@kernel.org> <20201026091554.GB1154158@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "paulus@samba.org" , "pavel@ucw.cz" , "hpa@zytor.com" , "sparclinux@vger.kernel.org" , "cl@linux.com" , "will@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "x86@kernel.org" , "rppt@linux.ibm.com" , "borntraeger@de.ibm.com" , "mingo@redhat.com" , "rientjes@google.com" , "Brown, Len" , "aou@eecs.berkeley.edu" , "gor@linux.ibm.com" , "linux-pm@vger.kernel.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "tglx@linutronix.de" , "iamjoonsoo.kim@lge.com" , "linux-arm-kernel@lists.infradead.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , "palmer@dabbelt.com" , "akpm@linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , "davem@davemloft.net" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Oct 26, 2020 at 06:57:32PM +0000, Edgecombe, Rick P wrote: > On Mon, 2020-10-26 at 11:15 +0200, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 12:38:32AM +0000, Edgecombe, Rick P wrote: > > > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > > > From: Mike Rapoport > > > > > > > > When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page > > > > may > > > > be > > > > not present in the direct map and has to be explicitly mapped > > > > before > > > > it > > > > could be copied. > > > > > > > > On arm64 it is possible that a page would be removed from the > > > > direct > > > > map > > > > using set_direct_map_invalid_noflush() but __kernel_map_pages() > > > > will > > > > refuse > > > > to map this page back if DEBUG_PAGEALLOC is disabled. > > > > > > It looks to me that arm64 __kernel_map_pages() will still attempt > > > to > > > map it if rodata_full is true, how does this happen? > > > > Unless I misread the code, arm64 requires both rodata_full and > > debug_pagealloc_enabled() to be true for __kernel_map_pages() to do > > anything. > > But rodata_full condition applies to set_direct_map_*_noflush() as > > well, > > so with !rodata_full the linear map won't be ever changed. > > Hmm, looks to me that __kernel_map_pages() will only skip it if both > debug pagealloc and rodata_full are false. > > But now I'm wondering if maybe we could simplify things by just moving > the hibernate unmapped page logic off of the direct map. On x86, > text_poke() used to use this reserved fixmap pte thing that it could > rely on to remap memory with. If hibernate had some separate pte for > remapping like that, then we could not have any direct map restrictions > caused by it/kernel_map_pages(), and it wouldn't have to worry about > relying on anything else. Well, there is map_kernel_range() that can be used by hibernation as there is no requirement for particular virtual address, but that would be quite costly if done for every page. Maybe we can do somthing like if (kernel_page_present(s_page)) { do_copy_page(dst, page_address(s_page)); } else { map_kernel_range_noflush(page_address(page), PAGE_SIZE, PROT_READ, &page); do_copy_page(dst, page_address(s_page)); unmap_kernel_range_noflush(page_address(page), PAGE_SIZE); } But it seems that a prerequisite for changing the way a page is mapped in safe_copy_page() would be to teach hibernation that a mapping here may fail. -- Sincerely yours, Mike. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Rapoport Date: Tue, 27 Oct 2020 08:49:02 +0000 Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Message-Id: <20201027084902.GH1154158@kernel.org> List-Id: References: <20201025101555.3057-1-rppt@kernel.org> <20201025101555.3057-3-rppt@kernel.org> <20201026091554.GB1154158@kernel.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Edgecombe, Rick P" Cc: "benh@kernel.crashing.org" , "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "paulus@samba.org" , "pavel@ucw.cz" , "hpa@zytor.com" , "sparclinux@vger.kernel.org" , "cl@linux.com" , "will@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "mpe@ellerman.id.au" , "x86@kernel.org" , "rppt@linux.ibm.com" , "borntraeger@de.ibm.com" , "mingo@redhat.com" , "rientjes@google.com" , "Brown, Len" , "aou@eecs.berkeley.edu" , "gor@linux.ibm.com" , "linux-pm@vger.kernel.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "tglx@linutronix.de" , "iamjoonsoo.kim@lge.com" , "linux-arm-kernel@lists.infradead.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , "palmer@dabbelt.com" , "akpm@linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , "davem@davemloft.net" On Mon, Oct 26, 2020 at 06:57:32PM +0000, Edgecombe, Rick P wrote: > On Mon, 2020-10-26 at 11:15 +0200, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 12:38:32AM +0000, Edgecombe, Rick P wrote: > > > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > > > From: Mike Rapoport > > > > > > > > When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page > > > > may > > > > be > > > > not present in the direct map and has to be explicitly mapped > > > > before > > > > it > > > > could be copied. > > > > > > > > On arm64 it is possible that a page would be removed from the > > > > direct > > > > map > > > > using set_direct_map_invalid_noflush() but __kernel_map_pages() > > > > will > > > > refuse > > > > to map this page back if DEBUG_PAGEALLOC is disabled. > > > > > > It looks to me that arm64 __kernel_map_pages() will still attempt > > > to > > > map it if rodata_full is true, how does this happen? > > > > Unless I misread the code, arm64 requires both rodata_full and > > debug_pagealloc_enabled() to be true for __kernel_map_pages() to do > > anything. > > But rodata_full condition applies to set_direct_map_*_noflush() as > > well, > > so with !rodata_full the linear map won't be ever changed. > > Hmm, looks to me that __kernel_map_pages() will only skip it if both > debug pagealloc and rodata_full are false. > > But now I'm wondering if maybe we could simplify things by just moving > the hibernate unmapped page logic off of the direct map. On x86, > text_poke() used to use this reserved fixmap pte thing that it could > rely on to remap memory with. If hibernate had some separate pte for > remapping like that, then we could not have any direct map restrictions > caused by it/kernel_map_pages(), and it wouldn't have to worry about > relying on anything else. Well, there is map_kernel_range() that can be used by hibernation as there is no requirement for particular virtual address, but that would be quite costly if done for every page. Maybe we can do somthing like if (kernel_page_present(s_page)) { do_copy_page(dst, page_address(s_page)); } else { map_kernel_range_noflush(page_address(page), PAGE_SIZE, PROT_READ, &page); do_copy_page(dst, page_address(s_page)); unmap_kernel_range_noflush(page_address(page), PAGE_SIZE); } But it seems that a prerequisite for changing the way a page is mapped in safe_copy_page() would be to teach hibernation that a mapping here may fail. -- Sincerely yours, Mike. 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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 AC3B1C4363A for ; Tue, 27 Oct 2020 08:49:57 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 46A34207DE for ; Tue, 27 Oct 2020 08:49:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="0HIfGgYT"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cob/039d" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46A34207DE Authentication-Results: mail.kernel.org; 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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXKfV-0004GA-6Q; Tue, 27 Oct 2020 08:49:25 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXKfO-0004Dr-EY; Tue, 27 Oct 2020 08:49:19 +0000 Received: from kernel.org (unknown [87.70.96.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 817B6207DE; Tue, 27 Oct 2020 08:49:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603788557; bh=vqvHVfwUem4JOBq/WXsfNE79L5Iz5nEhnMlkJj2ElFU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cob/039dcWnn8OjH5If0m1K0e5hz+wi7uaTqafHhMC0w6AKDJ7mof/L9QVAWjAi5m AzwVpAcX/G3bIeFGz/QZ6LDXFrWjC3A32wjsC/UaCx/T35y4jeNZtg1G5OqKcQamFp mFhuBk5Uhn3ItuoN/wmMtQFg0IPWtBPQaAK5nUZY= Date: Tue, 27 Oct 2020 10:49:02 +0200 From: Mike Rapoport To: "Edgecombe, Rick P" Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Message-ID: <20201027084902.GH1154158@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> <20201025101555.3057-3-rppt@kernel.org> <20201026091554.GB1154158@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201027_044918_795560_03DEF45A X-CRM114-Status: GOOD ( 27.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "benh@kernel.crashing.org" , "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "paulus@samba.org" , "pavel@ucw.cz" , "hpa@zytor.com" , "sparclinux@vger.kernel.org" , "cl@linux.com" , "will@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "mpe@ellerman.id.au" , "x86@kernel.org" , "rppt@linux.ibm.com" , "borntraeger@de.ibm.com" , "mingo@redhat.com" , "rientjes@google.com" , "Brown, Len" , "aou@eecs.berkeley.edu" , "gor@linux.ibm.com" , "linux-pm@vger.kernel.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "tglx@linutronix.de" , "iamjoonsoo.kim@lge.com" , "linux-arm-kernel@lists.infradead.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , "palmer@dabbelt.com" , "akpm@linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , "davem@davemloft.net" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Oct 26, 2020 at 06:57:32PM +0000, Edgecombe, Rick P wrote: > On Mon, 2020-10-26 at 11:15 +0200, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 12:38:32AM +0000, Edgecombe, Rick P wrote: > > > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > > > From: Mike Rapoport > > > > > > > > When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page > > > > may > > > > be > > > > not present in the direct map and has to be explicitly mapped > > > > before > > > > it > > > > could be copied. > > > > > > > > On arm64 it is possible that a page would be removed from the > > > > direct > > > > map > > > > using set_direct_map_invalid_noflush() but __kernel_map_pages() > > > > will > > > > refuse > > > > to map this page back if DEBUG_PAGEALLOC is disabled. > > > > > > It looks to me that arm64 __kernel_map_pages() will still attempt > > > to > > > map it if rodata_full is true, how does this happen? > > > > Unless I misread the code, arm64 requires both rodata_full and > > debug_pagealloc_enabled() to be true for __kernel_map_pages() to do > > anything. > > But rodata_full condition applies to set_direct_map_*_noflush() as > > well, > > so with !rodata_full the linear map won't be ever changed. > > Hmm, looks to me that __kernel_map_pages() will only skip it if both > debug pagealloc and rodata_full are false. > > But now I'm wondering if maybe we could simplify things by just moving > the hibernate unmapped page logic off of the direct map. On x86, > text_poke() used to use this reserved fixmap pte thing that it could > rely on to remap memory with. If hibernate had some separate pte for > remapping like that, then we could not have any direct map restrictions > caused by it/kernel_map_pages(), and it wouldn't have to worry about > relying on anything else. Well, there is map_kernel_range() that can be used by hibernation as there is no requirement for particular virtual address, but that would be quite costly if done for every page. Maybe we can do somthing like if (kernel_page_present(s_page)) { do_copy_page(dst, page_address(s_page)); } else { map_kernel_range_noflush(page_address(page), PAGE_SIZE, PROT_READ, &page); do_copy_page(dst, page_address(s_page)); unmap_kernel_range_noflush(page_address(page), PAGE_SIZE); } But it seems that a prerequisite for changing the way a page is mapped in safe_copy_page() would be to teach hibernation that a mapping here may fail. -- Sincerely yours, Mike. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel