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 966C4C43334 for ; Mon, 25 Jul 2022 06:47:16 +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-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=SYokYOAB7PnHakDqhLjrDV1vM4uZ0jeDwnTrzPkI8rc=; b=m5Zy7/kB43qFxx NZe+40a30hLcfQx2Jng6Lm6rSo1NXN0lvs6PfqQt8LYlGqU9YxPsaIBYiufcw5RoEECGEMfgUlPGm LOzUZ3/Xx69oE7aYcyBPeYbQRhB2OsXY5+X/vmjNbI5BSEBUDjH2CVPp7XBn9PMBrcZ3gcqG/MOAj ZZZVpaa/Lim8fStDR11EntetZl+YaK0u4uiFRqkZN/Q2yFHyTm9VF31LPJJiflRaMAhiJ9HqUSimj Ftfp93HqxlkfQsU5xDMOno2kG2gylwVBhe34BkjXAGXKW/qZpkQQSWZTIT6b59Cy7GRq4/EePZ12A DQ/XENJ+I9aXA+JjsOBg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oFrrA-005f1b-Ed; Mon, 25 Jul 2022 06:46:20 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oFrr6-005ewt-Vu for linux-arm-kernel@lists.infradead.org; Mon, 25 Jul 2022 06:46:18 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 91D47610A1; Mon, 25 Jul 2022 06:46:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBF0EC341C7; Mon, 25 Jul 2022 06:46:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1658731575; bh=hIZrYAxn265ebgeF7Bwq7AWTsRMM8aNkjPhwdYrVvPo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=osNv7G6brArIxFH6QeFgaRQ6faY2Q0HTiCZ1w/P+kGwwRNfXEJMAHrbYdJY2g1aFa qHTyjZ/CCqMxNbJd6JjQSSBfbLFbXr7PAtJKicGfARZgvm/uATPZ9KNmKkophIW5lo XdagoKwJqC3B78lYz417IQxdGlnTr/RiojJn2nBPN9GOwtJ17VSDxlkZFtfdqPlr9U BienTQy1Fcxw2C1faujgJCrzJdQXrwhaKOtLnaitvQe50I44I6mQqR+0rnwfHQk/SC iKl7uAedh7x2u8PAJqiGQnIfoII+C6ypUkQAP7GARtMT/Cd7hYryBlytp56Vh/4lqh M5fNWDCiB67rw== Date: Mon, 25 Jul 2022 09:46:04 +0300 From: Mike Rapoport To: Will Deacon Cc: "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, geert+renesas@glider.be, ardb@kernel.org, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com Subject: Re: [PATCH v5] arm64: mm: fix linear mem mapping access performance degradation Message-ID: References: <1657460657-25698-1-git-send-email-guanghuifeng@linux.alibaba.com> <20220718131005.GA12406@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220718131005.GA12406@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220724_234617_082764_227CEA5A X-CRM114-Status: GOOD ( 24.36 ) 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="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, Jul 18, 2022 at 02:10:06PM +0100, Will Deacon wrote: > On Sun, Jul 10, 2022 at 11:33:02PM +0800, guanghui.fgh wrote: > > In short, this path work: > > > > 1.Before doing work for rebuiling crashkernel mem, the pgd is swapper_pg_dir > > in [[[ttbr1]]] > > > > 2.Change the [[[ttbr0]]]to use idmap_pg_dir pgd > > > > 3.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] are mapped [[[only]]] > > with idmap_pg_dir mapping in [[[ttbr0]]] > > > > 4.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] will flush tlb all, > > switch [[[ttbr1]]] to use init_pg_dir pgd(and flush tlb all again). > > There is no tlb conflict to swapper_pg_dir. > > There is no tlb cache for swapper_pg_dir. > > > > 5.Woring with init_pg_dir pgd to access swapper_pg_dir pagetable with fix > > mapping. And modify crashkernel mapping in the swapper_pg_dir without any > > tlb conflict and flush. > > > > 6.When finishing the work, switch ttbr1 pgd to the origin swapper_pg_dir > > with cpu_replace_ttbr1 function(similar to the above). > > I do not think that this complexity is justified. As I have stated on > numerous occasions already, I would prefer that we leave the crashkernel > mapped when rodata is not "full". That fixes your performance issue and > matches what we do for module code, so I do not see a security argument > against it. The protection of the crash kernel is not about security. This is about an ability to do post mortem with kdump and such when the things go awry. I think it's possible to have both large pages in the linear map and the protection of crash kernel in much simpler way that this patch does, I'll try to send an RFC Really Soon. > I do not plan to merge this patch as-is. > > Thanks, > > Will -- Sincerely yours, Mike. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel