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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 4B704C49EA5 for ; Thu, 24 Jun 2021 10:47:41 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E5CB461418 for ; Thu, 24 Jun 2021 10:47:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5CB461418 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BFC2E6B0036; Thu, 24 Jun 2021 06:47:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BAC3E6B005D; Thu, 24 Jun 2021 06:47:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A73EA6B006C; Thu, 24 Jun 2021 06:47:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0218.hostedemail.com [216.40.44.218]) by kanga.kvack.org (Postfix) with ESMTP id 67E1E6B0036 for ; Thu, 24 Jun 2021 06:47:39 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 9B4A8180278DC for ; Thu, 24 Jun 2021 10:47:39 +0000 (UTC) X-FDA: 78288291438.24.341C20A Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf14.hostedemail.com (Postfix) with ESMTP id 09288C00CBFA for ; Thu, 24 Jun 2021 10:47:38 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3A05231B; Thu, 24 Jun 2021 03:47:38 -0700 (PDT) Received: from [10.57.9.136] (unknown [10.57.9.136]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6E5F73F718; Thu, 24 Jun 2021 03:47:36 -0700 (PDT) Subject: Re: [PATCH RFC 0/2] dma-pool: allow user to disable atomic pool To: Baoquan He , Christoph Hellwig Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, rientjes@google.com, rppt@linux.ibm.com, thomas.lendacky@amd.com, brijesh.singh@amd.com, kexec@lists.infradead.org, iommu@lists.linux-foundation.org, m.szyprowski@samsung.com References: <20210624052010.5676-1-bhe@redhat.com> <20210624092930.GA802261@MiWiFi-R3L-srv> From: Robin Murphy Message-ID: <8b3d4e02-6e94-ad59-a480-fed8e55c009a@arm.com> Date: Thu, 24 Jun 2021 11:47:31 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210624092930.GA802261@MiWiFi-R3L-srv> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Authentication-Results: imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of robin.murphy@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=robin.murphy@arm.com; dmarc=pass (policy=none) header.from=arm.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 09288C00CBFA X-Stat-Signature: 7gix7f6dwiohxz3w9gka1wrc17jzquhk X-HE-Tag: 1624531658-393540 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 2021-06-24 10:29, Baoquan He wrote: > On 06/24/21 at 08:40am, Christoph Hellwig wrote: >> So reduce the amount allocated. But the pool is needed for proper >> operation on systems with memory encryption. And please add the right >> maintainer or at least mailing list for the code you're touching next >> time. > > Oh, I thoutht it's memory issue only, should have run > ./scripts/get_maintainer.pl. sorry. > > About reducing the amount allocated, it may not help. Because on x86_64, > kdump kernel doesn't put any page of memory into buddy allocator of DMA > zone. Means it will defenitely OOM for atomic_pool_dma initialization. > > Wondering in which case or on which device the atomic pool is needed on > AMD system with mem encrytion enabled. As we can see, the OOM will > happen too in kdump kernel on Intel system, even though it's not > necessary. Hmm, I think the Kconfig reshuffle has actually left a slight wrinkle here. For DMA_DIRECT_REMAP=y we can assume an atomic pool is always needed, since that was the original behaviour anyway. However the implications of AMD_MEM_ENCRYPT=y are different - even if support is enabled, it still should only be relevant if mem_encrypt_active(), so it probably does make sense to have an additional runtime gate on that. From a quick scan, use of dma_alloc_from_pool() already depends on force_dma_unencrypted() so that's probably fine already, but I think we'd need a bit of extra protection around dma_free_from_pool() to prevent gen_pool_has_addr() dereferencing NULL if the pools are uninitialised, even with your proposed patch as it is. Presumably nothing actually called dma_direct_free() when you tested this? Robin.