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Thu, 25 Aug 2022 03:35:11 -0400 X-MC-Unique: ZtJcIqVGOgGj1CQMWQiYuw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6DCB53C10682; Thu, 25 Aug 2022 07:35:10 +0000 (UTC) Received: from localhost (ovpn-13-108.pek2.redhat.com [10.72.13.108]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 905CB2166B26; Thu, 25 Aug 2022 07:35:09 +0000 (UTC) Date: Thu, 25 Aug 2022 15:35:04 +0800 From: Baoquan He To: Mike Rapoport Cc: linux-arm-kernel@lists.infradead.org, Ard Biesheuvel , kexec@lists.infradead.org, Catalin Marinas , Guanghui Feng , Mark Rutland , Mike Rapoport , Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mike Rapoport Subject: Re: [PATCH 0/5] arm64/mm: remap crash kernel with base pages even if rodata_full disabled Message-ID: References: <20220819041156.873873-1-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220819041156.873873-1-rppt@kernel.org> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661412915; a=rsa-sha256; cv=none; b=8GqEyEl8bZkehS6S5QqrdrfjckD7QH9+NMdHCTTAONYKT8cq1dj6J210TSgPEv0QRj7Cjv kAQPHWhRABr1Ax4T+5KJIghpyP5/0qsdTOsQLQ/fciNdnYb4hB3oV66vYD5xx8PzZMy4OG cACjNkTO+Oyt/lsubhMaOAcSZgWOB9I= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="Q3K/ktaL"; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf12.hostedemail.com: domain of bhe@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=bhe@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661412915; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=/KHHMrmA8HFk2ILFS/S3jVPvSPT7uexAlYEbMs4sA0E=; b=psdvEzq8sIKYxUwhx43ZyAsEbZrmbjCpFiHtvdonRUVjIv9OOQ81nRxqAi5Yh29Qn+VF1o FP+s+R9Rv03fhHeauu5hktgDuCs4FAZ9fQjWwV/jMX+syWazPvMfE71VHL9Q0YxTpLzdIs bKDiVh6n0tUhL8yECsknEaAYqIC6gGk= Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="Q3K/ktaL"; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf12.hostedemail.com: domain of bhe@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=bhe@redhat.com X-Rspam-User: X-Rspamd-Queue-Id: 2F42F40004 X-Rspamd-Server: rspam08 X-Stat-Signature: cdadmbmdmeary4yhuks6ehgea3pmbp95 X-HE-Tag: 1661412915-127983 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: Add kexec list in CC On 08/19/22 at 07:11am, Mike Rapoport wrote: > From: Mike Rapoport > > Hi, > > There were several rounds of discussion how to remap with base pages only > the crash kernel area, the latest one here: > > https://lore.kernel.org/all/1656777473-73887-1-git-send-email-guanghuifeng@linux.alibaba.com > > and this is my attempt to allow having both large pages in the linear map > and protection for the crash kernel memory. > > For server systems it is important to protect crash kernel memory for > post-mortem analysis, and for that protection to work the crash kernel > memory should be mapped with base pages in the linear map. > > On the systems with ZONE_DMA/DMA32 enabled, crash kernel reservation > happens after the linear map is created and the current code forces using > base pages for the entire linear map, which results in performance > degradation. > > These patches enable remapping of the crash kernel area with base pages > while keeping large pages in the rest of the linear map. > > The idea is to align crash kernel reservation to PUD boundaries, remap that > PUD and then free the extra memory. Hi Mike, Thanks for the effort to work on this issue. While I have to say this isnt's good because it can only be made relying on a prerequisite that there's big enough memory. If on a system, say 2G memory, it's not easy to succeed on getting one 1G memory. While we only require far smaller region than 1G, e.g about 200M which should be easy to get. So the way taken in this patchset is too quirky and will cause regression on systemswith small memory. This kind of sytems with small memory exists widely on virt guest instance. The crashkernel reservation happens after linear map because the reservation needs to know the dma zone boundary, arm64_dma_phys_limit. If we can deduce that before bootmem_init(), the reservation can be done before linear map. I will make an attempt on that. If still can't be accepted, we would like to take off the crashkernel region protection on arm64 for now. Thanks Baoquan