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Tue, 05 Jul 2022 04:35:24 -0400 X-MC-Unique: uU9BWdGCPfue2BuqLtC7dg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C311C85A581; Tue, 5 Jul 2022 08:35:23 +0000 (UTC) Received: from localhost (ovpn-13-74.pek2.redhat.com [10.72.13.74]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 393584010D28; Tue, 5 Jul 2022 08:35:22 +0000 (UTC) Date: Tue, 5 Jul 2022 16:35:18 +0800 From: Baoquan He To: Ard Biesheuvel Cc: Will Deacon , kexec@lists.infradead.org, "guanghui.fgh" , 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 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Message-ID: 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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220705_013539_225206_BEC7B1D7 X-CRM114-Status: GOOD ( 30.77 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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Tue, 05 Jul 2022 04:35:24 -0400 X-MC-Unique: uU9BWdGCPfue2BuqLtC7dg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C311C85A581; Tue, 5 Jul 2022 08:35:23 +0000 (UTC) Received: from localhost (ovpn-13-74.pek2.redhat.com [10.72.13.74]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 393584010D28; Tue, 5 Jul 2022 08:35:22 +0000 (UTC) Date: Tue, 5 Jul 2022 16:35:18 +0800 From: Baoquan He To: Ard Biesheuvel Cc: Will Deacon , kexec@lists.infradead.org, "guanghui.fgh" , 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 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Message-ID: 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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220705_013538_852911_E79C6460 X-CRM114-Status: GOOD ( 31.58 ) 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-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org T24gMDcvMDQvMjIgYXQgMDc6MDlwbSwgQXJkIEJpZXNoZXV2ZWwgd3JvdGU6Cj4gT24gTW9uLCA0 IEp1bCAyMDIyIGF0IDE4OjM4LCBXaWxsIERlYWNvbiA8d2lsbEBrZXJuZWwub3JnPiB3cm90ZToK PiA+Cj4gPiBPbiBNb24sIEp1bCAwNCwgMjAyMiBhdCAxMDozNDowN1BNICswODAwLCBndWFuZ2h1 aS5mZ2ggd3JvdGU6Cj4gPiA+IFRoYW5rcy4KPiA+ID4KPiA+ID4g5ZyoIDIwMjIvNy80IDIyOjIz LCBXaWxsIERlYWNvbiDlhpnpgZM6Cj4gPiA+ID4gT24gTW9uLCBKdWwgMDQsIDIwMjIgYXQgMTA6 MTE6MjdQTSArMDgwMCwgZ3VhbmdodWkuZmdoIHdyb3RlOgo+IC4uLgo+ID4gPiA+ID4gTmFtZWx5 LCBpdCdzIG5lZWQgdG8gdXNlIG5vbiBibG9jay9zZWN0aW9uIG1hcHBpbmcgZm9yIGNyYXNoa2Vy bmVsIG1lbQo+ID4gPiA+ID4gYmVmb3JlIHNocmluZ2tpbmcuCj4gPiA+ID4KPiA+ID4gPiBXZWxs LCB5ZXMsIGJ1dCB3ZSBjYW4gY2hhbmdlIGFyY2hfa2V4ZWNfW3VuXXByb3RlY3RfY3Jhc2hrcmVz KCkgbm90IHRvIGRvCj4gPiA+ID4gdGhhdCBpZiB3ZSdyZSBsZWF2aW5nIHRoZSB0aGluZyBtYXBw ZWQsIG5vPwo+ID4gPiA+Cj4gPiA+IEkgdGhpbmsgd2Ugc2hvdWxkIHVzZSBhcmNoX2tleGVjX1t1 bl1wcm90ZWN0X2NyYXNoa3JlcyBmb3IgY3Jhc2hrZXJuZWwgbWVtLgo+ID4gPgo+ID4gPiBCZWNh dXNlIHdoZW4gaW52YWxpZCBjcmFzaGtlcm5lbCBtZW0gcGFnZXRhYmxlLCB0aGVyZSBpcyBubyBj aGFuY2UgdG8gcmQvd3IKPiA+ID4gdGhlIGNyYXNoa2VybmVsIG1lbSBieSBtaXN0YWtlLgo+ID4g Pgo+ID4gPiBJZiB3ZSBkb24ndCB1c2UgYXJjaF9rZXhlY19bdW5dcHJvdGVjdF9jcmFzaGtyZXMg dG8gaW52YWxpZCBjcmFzaGtlcm5lbCBtZW0KPiA+ID4gcGFnZXRhYmxlLCB0aGVyZSBtYXliZSBz b21lIHdyaXRlIG9wZXJhdGlvbnMgdG8gdGhlc2UgbWVtIGJ5IG1pc3Rha2Ugd2hpY2gKPiA+ID4g bWF5IGNhdXNlIGNyYXNoa2VybmVsIGJvb3QgZXJyb3IgYW5kIHZtY29yZSBzYXZpbmcgZXJyb3Iu Cj4gPgo+ID4gSSBkb24ndCByZWFsbHkgYnV5IHRoaXMgbGluZSBvZiByZWFzb25pbmcuIFRoZSBl bnRpcmUgbWFpbiBrZXJuZWwgaXMKPiA+IHdyaXRhYmxlLCBzbyB3aHkgZG8gd2UgY2FyZSBhYm91 dCBwcm90ZWN0aW5nIHRoZSBjcmFzaGtlcm5lbCBzbyBtdWNoPyBUaGUKPiA+IF9jb2RlXyB0byBs YXVuY2ggdGhlIGNyYXNoIGtlcm5lbCBpcyB3cml0YWJsZSEgSWYgeW91IGNhcmUgYWJvdXQgcHJl dmVudGluZwo+ID4gd3JpdGVzIHRvIG1lbW9yeSB3aGljaCBzaG91bGQgbm90IGJlIHdyaXRhYmxl LCB0aGVuIHlvdSBzaG91bGQgdXNlCj4gPiByb2RhdGE9ZnVsbC4KPiA+Cj4gCj4gVGhpcyBpcyBu b3QgZW50aXJlbHkgdHJ1ZSAtIHRoZSBjb3JlIGtlcm5lbCB0ZXh0IGFuZCByb2RhdGEgYXJlCj4g cmVtYXBwZWQgci9vIGluIHRoZSBsaW5lYXIgbWFwLCB3aGVyZWFzIGFsbCBtb2R1bGUgY29kZSBh bmQgcm9kYXRhIGFyZQo+IGxlZnQgd3JpdGFibGUgd2hlbiByb2RhdGEgIT0gZnVsbC4KPiAKPiBC dXQgdGhlIGNvbmNsdXNpb24gaXMgdGhlIHNhbWUsIGltbzogaWYgeW91IGNhbid0IGJlIGJvdGhl cmVkIHRvCj4gcHJvdGVjdCBhIGdvb2QgY2h1bmsgb2YgdGhlIGNvZGUgYW5kIHJvZGF0YSB0aGF0 IHRoZSBrZXJuZWwgcmVsaWVzIG9uLAo+IHdoeSBzaG91bGQgdGhlIGNyYXNoa2VybmVsIGJlIHRy ZWF0ZWQgYW55IGRpZmZlcmVudGx5PwoKS2VybmVsIHRleHQgYW5kIHJvZGF0YSBhcmUgcmVtYXBw ZWQgci9vIGluIGxpbmVhciBtYXAsIHdoZXJlYXMKbW9kdWxlIGNvZGUgYW5kIHJvZGF0YSBhcmUg bGVmdCB3cml0YWJsZSwgaXQncyBkaWZmZXJlbnQgY29uY2VwdAp0aGFuIGNyYXNoa2VybmVsIHJl Z2lvbiBiZWluZyBtYXBwZWQgci9vLgoKSWYgaXQncyBkb2FibGUgaW4gdGVjaG5vbG9neSB0byBy ZW1hcCBtb2R1bGUgY29kZSBhbmQgcm9kYXRhIHIvbywgYW5kCnN0YW1waW5nIGludG8gdGhvc2Ug cmVnaW9ucyB3aWxsIGNvcnJ1cHQgdGhlIGVudGlyZSBzeXN0ZW0sIHdlIHNob3VsZCBkbwppdCB0 b28uIEhvd2V2ZXIsIGtkdW1wIGlzIGEgc3lzdGVtIGVycm9yIGRpYWdvbm9zaW5nIG1lY2hhbmlz bSB3aGljaCBpcwp2ZXJ5IGltcG9ydGFudCBhbmQgaGVscGZ1bCBvbiBzZXJ2ZXIsIG9yIHNvbWUg YXBwbGljYXRpb24gc2NlbmFyaW9zLCBlLmcKY2xvdWQuIFN0YW1waW5nIGludG8gY3Jhc2hrZXJu ZWwgcmVnaW9uIHdpbGwgbWFrZSBpdCB1c2VsZXNzLgoKSSBhbSBub3QgYWdhaW5zdCByZW1vdmlu ZyB0aGUgYXJjaF9rZXhlY19bdW5dcHJvdGVjdF9jcmFzaGtyZXMgb24gYXJtNjQuCkl0IGlzIGEg YmFsYW5jZToKClByb3RlY3RpbmcgdGhlIGNyYXNoa2VybmVsIHJlZ2lvbiwgY2F1c2Vpbmcgc2V2 ZXJlIHBlcmZvcm1hbmNlCmRlZ3JhZGF0aW9uLiBUaGlzIGlzIGFsd2F5cyBmZWx0IHNpbmNlIHdl IHVzdWFsbHkgZG9uJ3Qgc3BlY2lmeSByb2RhdGEKYW5kIGVuYWJsZSBrZmVuY2UuCgpUYWtpbmcg b2ZmIHRoZSBwcm90ZWN0aW5nIG9mIGNyYXNoa2VybmVsIHJlZ2lvbiwgcGVyZm9ybWFuY2UgaW1w cm92ZWQKdmVyeSBtdWNoLCB3aGlsZSB3cm9uZyBjb2RlIG1heSBzdGFtcCBpbnRvIGNyYXNoa2Vy bmVsIHJlZ2lvbiBhbmQgZmFpbAprZHVtcC4gVGhhdCBjb3VsZCBoYXBwZW4gb25lIGluIGEgbWls bGlvbi4gT25jZSBoYXBwZW4sIGl0J3MgYSBuaWdodG1hcmUKb2Yga2VybmVsIGRldi4KCgpfX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpsaW51eC1hcm0ta2Vy bmVsIG1haWxpbmcgbGlzdApsaW51eC1hcm0ta2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0 cDovL2xpc3RzLmluZnJhZGVhZC5vcmcvbWFpbG1hbi9saXN0aW5mby9saW51eC1hcm0ta2VybmVs Cg== 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 333CFC43334 for ; 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Tue, 5 Jul 2022 08:35:23 +0000 (UTC) Received: from localhost (ovpn-13-74.pek2.redhat.com [10.72.13.74]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 393584010D28; Tue, 5 Jul 2022 08:35:22 +0000 (UTC) Date: Tue, 5 Jul 2022 16:35:18 +0800 From: Baoquan He To: Ard Biesheuvel Cc: Will Deacon , kexec@lists.infradead.org, "guanghui.fgh" , 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 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; 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s=arc-20220608; d=hostedemail.com; t=1657010136; a=rsa-sha256; cv=none; b=7JRdeCZ0WvTRqcbE5VndRPi45hxPVvSoGnxoFFmgI7IY5uyduaMMVXkOJNCHj9x841gx42 NHqsn3fL/UBHbZQqczaSviw1ef950pdr/e+fmZLQIbiAuHaQ/I53ga8GwcCpBQQyliM8Bl Kq+y6H9NeAd3qah6EDcK7QGwoJw3oek= X-Rspam-User: X-Rspamd-Queue-Id: B0BCA40011 Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=cG4nakGB; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf07.hostedemail.com: domain of bhe@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=bhe@redhat.com X-Stat-Signature: cyfyuk4fpsmjzj7c6jskfzpj5u96argf X-Rspamd-Server: rspam08 X-HE-Tag: 1657010135-296351 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: On 07/04/22 at 07:09pm, 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. > > 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? Kernel text and rodata are remapped r/o in linear map, whereas module code and rodata are left writable, it's different concept than crashkernel region being mapped r/o. If it's doable in technology to remap module code and rodata r/o, and stamping into those regions will corrupt the entire system, we should do it too. However, kdump is a system error diagonosing mechanism which is very important and helpful on server, or some application scenarios, e.g cloud. Stamping into crashkernel region will make it useless. I am not against removing the arch_kexec_[un]protect_crashkres on arm64. It is a balance: Protecting the crashkernel region, causeing severe performance degradation. This is always felt since we usually don't specify rodata and enable kfence. Taking off the protecting of crashkernel region, performance improved very much, while wrong code may stamp into crashkernel region and fail kdump. That could happen one in a million. Once happen, it's a nightmare of kernel dev.