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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 79A66C43334 for ; Tue, 5 Jul 2022 12:08:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=dxSFzM6dqy1DUrdwGKk817r2vNcjdDC3cr6k5zcd/zo=; b=rMQ8ZC0dJoxvbI 0jhQ783UOzUsiXmw63OOuBxBXKqAE8o3rK5Rxvb1sP/UIxlFX7wHz5v8xg6kpEiCHxadvwslXEtk1 O2VsDDdFibc9kUpgOIOc4WbAeVBvk2wnu08HLzyhQvhIUdnaRASYw3phnpdWlcLxog0bFfZzm3Akk q2t08IXElhbsJtbkMCADwltcVtizWFSX2Ctbr7hf0JPUdv45s1LYvGWpoHS8Ownr0j3ncJYxTN0ht TB8RpLTf5/FClMv7IGt2mN2PGGVgEp/bKccIfKY/+3ezc7ZIWXmyTXNjTT+9kGnucHn+o9BUXbv3f NksE8oI3XEMLDrq4mrrg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o8hKu-0002Pa-D6; Tue, 05 Jul 2022 12:07:24 +0000 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1o8hKo-0002LJ-8f for linux-arm-kernel@lists.infradead.org; Tue, 05 Jul 2022 12:07:21 +0000 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=guanghuifeng@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0VISK1LP_1657022828; Received: from 30.225.28.170(mailfrom:guanghuifeng@linux.alibaba.com fp:SMTPD_---0VISK1LP_1657022828) by smtp.aliyun-inc.com; Tue, 05 Jul 2022 20:07:09 +0800 Message-ID: <5d044fdd-a61a-d60f-d294-89e17de37712@linux.alibaba.com> Date: Tue, 5 Jul 2022 20:07:07 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation To: Will Deacon , Ard Biesheuvel Cc: baolin.wang@linux.alibaba.com, catalin.marinas@arm.com, akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com, james.morse@arm.com, quic_qiancai@quicinc.com, christophe.leroy@csgroup.eu, jonathan@marek.ca, mark.rutland@arm.com, thunder.leizhen@huawei.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, rppt@kernel.org, geert+renesas@glider.be, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com References: <20220704103523.GC31437@willie-the-truck> <73f0c53b-fd17-c5e9-3773-1d71e564eb50@linux.alibaba.com> <20220704111402.GA31553@willie-the-truck> <4accaeda-572f-f72d-5067-2d0999e4d00a@linux.alibaba.com> <20220704131516.GC31684@willie-the-truck> <2ae1cae0-ee26-aa59-7ed9-231d67194dce@linux.alibaba.com> <20220704142313.GE31684@willie-the-truck> <6977c692-78ca-5a67-773e-0389c85f2650@linux.alibaba.com> <20220704163815.GA32177@willie-the-truck> <20220705095231.GB552@willie-the-truck> From: "guanghui.fgh" In-Reply-To: <20220705095231.GB552@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220705_050718_497397_8EFB3EC4 X-CRM114-Status: GOOD ( 18.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: base64 Content-Type: text/plain; charset="utf-8"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org CgrlnKggMjAyMi83LzUgMTc6NTIsIFdpbGwgRGVhY29uIOWGmemBkzoKPiBPbiBNb24sIEp1bCAw NCwgMjAyMiBhdCAwNzowOToyM1BNICswMjAwLCBBcmQgQmllc2hldXZlbCB3cm90ZToKPj4gT24g TW9uLCA0IEp1bCAyMDIyIGF0IDE4OjM4LCBXaWxsIERlYWNvbiA8d2lsbEBrZXJuZWwub3JnPiB3 cm90ZToKPj4+Cj4+PiBPbiBNb24sIEp1bCAwNCwgMjAyMiBhdCAxMDozNDowN1BNICswODAwLCBn dWFuZ2h1aS5mZ2ggd3JvdGU6Cj4+Pj4gVGhhbmtzLgo+Pj4+Cj4+Pj4g5ZyoIDIwMjIvNy80IDIy OjIzLCBXaWxsIERlYWNvbiDlhpnpgZM6Cj4+Pj4+IE9uIE1vbiwgSnVsIDA0LCAyMDIyIGF0IDEw OjExOjI3UE0gKzA4MDAsIGd1YW5naHVpLmZnaCB3cm90ZToKPj4gLi4uCj4+Pj4+PiBOYW1lbHks IGl0J3MgbmVlZCB0byB1c2Ugbm9uIGJsb2NrL3NlY3Rpb24gbWFwcGluZyBmb3IgY3Jhc2hrZXJu ZWwgbWVtCj4+Pj4+PiBiZWZvcmUgc2hyaW5na2luZy4KPj4+Pj4KPj4+Pj4gV2VsbCwgeWVzLCBi dXQgd2UgY2FuIGNoYW5nZSBhcmNoX2tleGVjX1t1bl1wcm90ZWN0X2NyYXNoa3JlcygpIG5vdCB0 byBkbwo+Pj4+PiB0aGF0IGlmIHdlJ3JlIGxlYXZpbmcgdGhlIHRoaW5nIG1hcHBlZCwgbm8/Cj4+ Pj4+Cj4+Pj4gSSB0aGluayB3ZSBzaG91bGQgdXNlIGFyY2hfa2V4ZWNfW3VuXXByb3RlY3RfY3Jh c2hrcmVzIGZvciBjcmFzaGtlcm5lbCBtZW0uCj4+Pj4KPj4+PiBCZWNhdXNlIHdoZW4gaW52YWxp ZCBjcmFzaGtlcm5lbCBtZW0gcGFnZXRhYmxlLCB0aGVyZSBpcyBubyBjaGFuY2UgdG8gcmQvd3IK Pj4+PiB0aGUgY3Jhc2hrZXJuZWwgbWVtIGJ5IG1pc3Rha2UuCj4+Pj4KPj4+PiBJZiB3ZSBkb24n dCB1c2UgYXJjaF9rZXhlY19bdW5dcHJvdGVjdF9jcmFzaGtyZXMgdG8gaW52YWxpZCBjcmFzaGtl cm5lbCBtZW0KPj4+PiBwYWdldGFibGUsIHRoZXJlIG1heWJlIHNvbWUgd3JpdGUgb3BlcmF0aW9u cyB0byB0aGVzZSBtZW0gYnkgbWlzdGFrZSB3aGljaAo+Pj4+IG1heSBjYXVzZSBjcmFzaGtlcm5l bCBib290IGVycm9yIGFuZCB2bWNvcmUgc2F2aW5nIGVycm9yLgo+Pj4KPj4+IEkgZG9uJ3QgcmVh bGx5IGJ1eSB0aGlzIGxpbmUgb2YgcmVhc29uaW5nLiBUaGUgZW50aXJlIG1haW4ga2VybmVsIGlz Cj4+PiB3cml0YWJsZSwgc28gd2h5IGRvIHdlIGNhcmUgYWJvdXQgcHJvdGVjdGluZyB0aGUgY3Jh c2hrZXJuZWwgc28gbXVjaD8gVGhlCj4+PiBfY29kZV8gdG8gbGF1bmNoIHRoZSBjcmFzaCBrZXJu ZWwgaXMgd3JpdGFibGUhIElmIHlvdSBjYXJlIGFib3V0IHByZXZlbnRpbmcKPj4+IHdyaXRlcyB0 byBtZW1vcnkgd2hpY2ggc2hvdWxkIG5vdCBiZSB3cml0YWJsZSwgdGhlbiB5b3Ugc2hvdWxkIHVz ZQo+Pj4gcm9kYXRhPWZ1bGwuCj4+Pgo+Pgo+PiBUaGlzIGlzIG5vdCBlbnRpcmVseSB0cnVlIC0g dGhlIGNvcmUga2VybmVsIHRleHQgYW5kIHJvZGF0YSBhcmUKPj4gcmVtYXBwZWQgci9vIGluIHRo ZSBsaW5lYXIgbWFwLCB3aGVyZWFzIGFsbCBtb2R1bGUgY29kZSBhbmQgcm9kYXRhIGFyZQo+PiBs ZWZ0IHdyaXRhYmxlIHdoZW4gcm9kYXRhICE9IGZ1bGwuCj4gCj4gWWVzLCBzb3JyeSwgeW91J3Jl IHF1aXRlIHJpZ2h0LiBUaGUga2VybmVsIHRleHQgaXMgb25seSB3cml0YWJsZSBpZgo+IHJvZGF0 YT1vZmYuCj4gCj4gQnV0IEkgc3RpbGwgdGhpbmsgaXQgbWFrZXMgc2Vuc2UgdG8gcHJvdGVjdCB0 aGUgY3Jhc2hrZXJuZWwgb25seSBpZgo+IHJvZGF0YT1mdWxsICh3aGljaCBpcyB0aGUgZGVmYXVs dCBvbiBhcm02NCkgYXMgdGhpcyBhbGxvd3MgdXMgdG8gcmVseQo+IG9uIHBhZ2UgbWFwcGluZ3Mg YW5kIEkgdGhpbmsgZml0cyB3ZWxsIHdpdGggd2hhdCB3ZSBkbyBmb3IgbW9kdWxlcy4KPiAKPj4g QnV0IHRoZSBjb25jbHVzaW9uIGlzIHRoZSBzYW1lLCBpbW86IGlmIHlvdSBjYW4ndCBiZSBib3Ro ZXJlZCB0bwo+PiBwcm90ZWN0IGEgZ29vZCBjaHVuayBvZiB0aGUgY29kZSBhbmQgcm9kYXRhIHRo YXQgdGhlIGtlcm5lbCByZWxpZXMgb24sCj4+IHdoeSBzaG91bGQgdGhlIGNyYXNoa2VybmVsIGJl IHRyZWF0ZWQgYW55IGRpZmZlcmVudGx5Pwo+IAo+IFRoYW5rcy4KPiAKPiBXaWxsClRoYW5rcy4K CjEuVGhlIHJvZGF0YSBmdWxsIGlzIGhhcm0gdG8gdGhlIHBlcmZvcm1hbmNlIGFuZCBoYXMgYmVl biBkaXNhYmxlZCBpbi1ob3VzZS4KCjIuV2hlbiB1c2luZyBjcmFzaGtlcm5lbCB3aXRoIHJvZGF0 YSBub24gZnVsbCwgdGhlIGtlcm5lbCBhbHNvIHdpbGwgdXNlIApub24gYmxvY2svc2VjdGlvbiBt YXBwaW5nIHdoaWNoIGNhdXNlIGhpZ2ggZC1UTEIgbWlzcyBhbmQgZGVncmFkZSAKcGVyZm9ybWFu Y2UgZ3JlYXRseS4KVGhpcyBwYXRjaCBmaXggaXQgdG8gdXNlIGJsb2NrL3NlY3Rpb24gbWFwcGlu ZyBhcyBmYXIgYXMgcG9zc2libGUuCgpib29sIGNhbl9zZXRfZGlyZWN0X21hcCh2b2lkKQp7Cgly ZXR1cm4gcm9kYXRhX2Z1bGwgfHwgZGVidWdfcGFnZWFsbG9jX2VuYWJsZWQoKTsKfQoKbWFwX21l bToKaWYgKGNhbl9zZXRfZGlyZWN0X21hcCgpIHx8IElTX0VOQUJMRUQoQ09ORklHX0tGRU5DRSkp CglmbGFncyB8PSBOT19CTE9DS19NQVBQSU5HUyB8IE5PX0NPTlRfTUFQUElOR1M7CgozLldoZW4g cm9kYXRhIGZ1bGwgaXMgZGlzYWJsZWQsIGNyYXNoa2VybmVsIGFsc28gbmVlZCBwcm90ZWN0KGtl ZXAgCmFyY2hfa2V4ZWNfW3VuXXByb3RlY3RfY3Jhc2hrcmVzIHVzaW5nKS4KSSB0aGluayBjcmFz aGtlcm5lbCBzaG91bGQndCBkZXBlbmQgb24gcmFkYXRhIGZ1bGwoTWF5YmUgb3RoZXIgCmFyY2hp dGVjdHVyZSBkb24ndCBzdXBwb3J0IHJhZGF0YSBmdWxsIG5vdykuCgpUaGFua3MuCgpfX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpsaW51eC1hcm0ta2VybmVs IG1haWxpbmcgbGlzdApsaW51eC1hcm0ta2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDov L2xpc3RzLmluZnJhZGVhZC5vcmcvbWFpbG1hbi9saXN0aW5mby9saW51eC1hcm0ta2VybmVsCg== 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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2B38C43334 for ; Tue, 5 Jul 2022 12:07:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C406A6B0071; Tue, 5 Jul 2022 08:07:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BEDED6B0073; Tue, 5 Jul 2022 08:07:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ADD5D6B0074; Tue, 5 Jul 2022 08:07:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 9E9D66B0071 for ; Tue, 5 Jul 2022 08:07:16 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 713912142A for ; Tue, 5 Jul 2022 12:07:16 +0000 (UTC) X-FDA: 79652920872.22.A80D989 Received: from out30-42.freemail.mail.aliyun.com (out30-42.freemail.mail.aliyun.com [115.124.30.42]) by imf11.hostedemail.com (Postfix) with ESMTP id 9883140002 for ; Tue, 5 Jul 2022 12:07:14 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=guanghuifeng@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0VISK1LP_1657022828; Received: from 30.225.28.170(mailfrom:guanghuifeng@linux.alibaba.com fp:SMTPD_---0VISK1LP_1657022828) by smtp.aliyun-inc.com; Tue, 05 Jul 2022 20:07:09 +0800 Message-ID: <5d044fdd-a61a-d60f-d294-89e17de37712@linux.alibaba.com> Date: Tue, 5 Jul 2022 20:07:07 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation To: Will Deacon , Ard Biesheuvel Cc: baolin.wang@linux.alibaba.com, catalin.marinas@arm.com, akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com, james.morse@arm.com, quic_qiancai@quicinc.com, christophe.leroy@csgroup.eu, jonathan@marek.ca, mark.rutland@arm.com, thunder.leizhen@huawei.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, rppt@kernel.org, geert+renesas@glider.be, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com References: <20220704103523.GC31437@willie-the-truck> <73f0c53b-fd17-c5e9-3773-1d71e564eb50@linux.alibaba.com> <20220704111402.GA31553@willie-the-truck> <4accaeda-572f-f72d-5067-2d0999e4d00a@linux.alibaba.com> <20220704131516.GC31684@willie-the-truck> <2ae1cae0-ee26-aa59-7ed9-231d67194dce@linux.alibaba.com> <20220704142313.GE31684@willie-the-truck> <6977c692-78ca-5a67-773e-0389c85f2650@linux.alibaba.com> <20220704163815.GA32177@willie-the-truck> <20220705095231.GB552@willie-the-truck> From: "guanghui.fgh" In-Reply-To: <20220705095231.GB552@willie-the-truck> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657022836; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dEo3fJ82q5V0WI5GhGs+XeSrJK7XasoOVAGb5QgknqE=; b=SPvcGrHRocaQtlENRyels4jFRYhSmjMgT/myPppYEa59gGa1DVloGhKWHKbzYq5Co9+IHA brIH+Q0NO2S4Z1XMSv3eytyHGYuadhaFU+6tayhIZ4OPWZ/bwY6bo5pVE1xEHBmpTDHsPc kKbb7JT5FKqnlLirIKIGXQgSRkQdSbY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657022836; a=rsa-sha256; cv=none; b=53OM3ltWIduVUUw07QWo1v7loiyb53i36W0Hbaqbb1fNwBew3gXnLRQIyu1X+vp/7CtNFy XQlJM41eqQWVSARhFDq+qdCYrJNl/Yrj6CH9v3OLxNTa7JfziGbdcq7UQPtrSXQOZQnvvg TtEBYDx7RjdoO5vZa0FjWdObD6TIaTU= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf11.hostedemail.com: domain of guanghuifeng@linux.alibaba.com designates 115.124.30.42 as permitted sender) smtp.mailfrom=guanghuifeng@linux.alibaba.com X-Stat-Signature: gdnbfi3en3iq7h195h6k99pzp44tq88t X-Rspamd-Queue-Id: 9883140002 X-Rspam-User: Authentication-Results: imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf11.hostedemail.com: domain of guanghuifeng@linux.alibaba.com designates 115.124.30.42 as permitted sender) smtp.mailfrom=guanghuifeng@linux.alibaba.com X-Rspamd-Server: rspam06 X-HE-Tag: 1657022834-476087 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 在 2022/7/5 17:52, Will Deacon 写道: > On Mon, Jul 04, 2022 at 07:09:23PM +0200, Ard Biesheuvel wrote: >> On Mon, 4 Jul 2022 at 18:38, Will Deacon wrote: >>> >>> On Mon, Jul 04, 2022 at 10:34:07PM +0800, guanghui.fgh wrote: >>>> Thanks. >>>> >>>> 在 2022/7/4 22:23, Will Deacon 写道: >>>>> On Mon, Jul 04, 2022 at 10:11:27PM +0800, guanghui.fgh wrote: >> ... >>>>>> Namely, it's need to use non block/section mapping for crashkernel mem >>>>>> before shringking. >>>>> >>>>> Well, yes, but we can change arch_kexec_[un]protect_crashkres() not to do >>>>> that if we're leaving the thing mapped, no? >>>>> >>>> I think we should use arch_kexec_[un]protect_crashkres for crashkernel mem. >>>> >>>> Because when invalid crashkernel mem pagetable, there is no chance to rd/wr >>>> the crashkernel mem by mistake. >>>> >>>> If we don't use arch_kexec_[un]protect_crashkres to invalid crashkernel mem >>>> pagetable, there maybe some write operations to these mem by mistake which >>>> may cause crashkernel boot error and vmcore saving error. >>> >>> I don't really buy this line of reasoning. The entire main kernel is >>> writable, so why do we care about protecting the crashkernel so much? The >>> _code_ to launch the crash kernel is writable! If you care about preventing >>> writes to memory which should not be writable, then you should use >>> rodata=full. >>> >> >> This is not entirely true - the core kernel text and rodata are >> remapped r/o in the linear map, whereas all module code and rodata are >> left writable when rodata != full. > > Yes, sorry, you're quite right. The kernel text is only writable if > rodata=off. > > But I still think it makes sense to protect the crashkernel only if > rodata=full (which is the default on arm64) as this allows us to rely > on page mappings and I think fits well with what we do for modules. > >> But the conclusion is the same, imo: if you can't be bothered to >> protect a good chunk of the code and rodata that the kernel relies on, >> why should the crashkernel be treated any differently? > > Thanks. > > Will Thanks. 1.The rodata full is harm to the performance and has been disabled in-house. 2.When using crashkernel with rodata non full, the kernel also will use non block/section mapping which cause high d-TLB miss and degrade performance greatly. This patch fix it to use block/section mapping as far as possible. bool can_set_direct_map(void) { return rodata_full || debug_pagealloc_enabled(); } map_mem: if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; 3.When rodata full is disabled, crashkernel also need protect(keep arch_kexec_[un]protect_crashkres using). I think crashkernel should't depend on radata full(Maybe other architecture don't support radata full now). Thanks.