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=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A374FC433B4 for ; Tue, 18 May 2021 23:45:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 29BE8610CB for ; Tue, 18 May 2021 23:45:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 29BE8610CB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8B59E6B010F; Tue, 18 May 2021 19:45:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 867046B0110; Tue, 18 May 2021 19:45:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6E0DC6B0111; Tue, 18 May 2021 19:45:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0167.hostedemail.com [216.40.44.167]) by kanga.kvack.org (Postfix) with ESMTP id 3869E6B010F for ; Tue, 18 May 2021 19:45:13 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id C54A5B9EB for ; Tue, 18 May 2021 23:45:12 +0000 (UTC) X-FDA: 78155985264.06.DC9C121 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf09.hostedemail.com (Postfix) with ESMTP id ADA7B600010A for ; Tue, 18 May 2021 23:45:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1621381511; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NyB3nRYXEIw9i58PAbApIYiWHD6bmSqOFX83eNLmrgQ=; b=A2azpbbzdV/hO2S7UbDnm1Fx2eXKsptBL034xKb3UlLDkbq81PQhDZoUD4pgiUcK6YbySp XAV6Hn5WoWOcGs+xbPOZraJ7jR6wdTngSdwgpPkXNVruH7qkCECWrI5UYYCTXVCwBM+k5p 7y6JT25I5ausTL1NAx1XNt1E63DVrKY= Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-1-tb1nGuusOgGbBpeQ03oj8g-1; Tue, 18 May 2021 19:45:08 -0400 X-MC-Unique: tb1nGuusOgGbBpeQ03oj8g-1 Received: by mail-qv1-f72.google.com with SMTP id d9-20020a0ce4490000b02901f0bee07112so2455966qvm.7 for ; Tue, 18 May 2021 16:45:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=NyB3nRYXEIw9i58PAbApIYiWHD6bmSqOFX83eNLmrgQ=; b=H9lyr4MLjNjGjkIU84OS5m3zTHcVer1rB3Dyg/njib5AQWqN4ZMnWCkf3C+H6B9odT D/IgGcnip/KGdjl0hGdHziuhdGe77tp0lSLxmuFpcMEqMe2lyq/bwI49skcpxcYLNeEg DY5pVyvrBudDQqPTe0ffFhMyes2IbJTWiFLFfTNn16+nHa4YE3nPf5Fwic2G5/PzoS2M 9EbaZbpeKV2qvGH4Ob/xAmc9DlGGoe/ha9QabTJGBH2JbbdSY1EwSuUo890lYtr+uHW8 WbpQH54dry1Re3BNa5C7+xAgPThxseePTPUNiQrpO2YOtYS76sR5L7fG33u5/pRAh8Pz IHJA== X-Gm-Message-State: AOAM530BJz26/ewllTnp/ZLGS6HhA7kkcPXTS7PKoDzQ0Yo1nHVcgrBC Y4fif6GAFpCPh5fflM+RFTgI9p48X4QUqe93ET+xZg63M3EGUV4eU+gmGVhQIDXGAj5DNZYTtKX RIGvJMKxgG90= X-Received: by 2002:a05:622a:350:: with SMTP id r16mr7491993qtw.27.1621381507346; Tue, 18 May 2021 16:45:07 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx7ExMzzZXtIx7iGUTcSpCi16S7VAiLXsFhzha61Te2cv+Okvdh1uyfL/4TjC80GU7c5+ldwA== X-Received: by 2002:a05:622a:350:: with SMTP id r16mr7491943qtw.27.1621381506771; Tue, 18 May 2021 16:45:06 -0700 (PDT) Received: from t490s (bras-base-toroon474qw-grc-72-184-145-4-219.dsl.bell.ca. [184.145.4.219]) by smtp.gmail.com with ESMTPSA id 7sm15927040qtu.38.2021.05.18.16.45.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 May 2021 16:45:06 -0700 (PDT) Date: Tue, 18 May 2021 19:45:05 -0400 From: Peter Xu To: Jason Gunthorpe Cc: Alistair Popple , linux-mm@kvack.org, nouveau@lists.freedesktop.org, bskeggs@redhat.com, akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, jhubbard@nvidia.com, rcampbell@nvidia.com, jglisse@redhat.com, hch@infradead.org, daniel@ffwll.ch, willy@infradead.org, bsingharora@gmail.com, Christoph Hellwig Subject: Re: [PATCH v8 5/8] mm: Device exclusive memory access Message-ID: References: <20210407084238.20443-1-apopple@nvidia.com> <20210407084238.20443-6-apopple@nvidia.com> <47694715.suB6H4Uo8R@nvdebian> <20210518173334.GE1002214@nvidia.com> <20210518194509.GF1002214@nvidia.com> <20210518230327.GG1002214@nvidia.com> MIME-Version: 1.0 In-Reply-To: <20210518230327.GG1002214@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: ADA7B600010A Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=A2azpbbz; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf09.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=peterx@redhat.com X-Rspamd-Server: rspam03 X-Stat-Signature: ioznwckfyyynu6k7cy6asex7f4buwsdj X-HE-Tag: 1621381511-826819 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 Tue, May 18, 2021 at 08:03:27PM -0300, Jason Gunthorpe wrote: > Logically during fork all these device exclusive pages should be > reverted back to their CPU pages, write protected and the CPU page PTE > copied to the fork. > > We should not copy the device exclusive page PTE to the fork. I think > I pointed to this on an earlier rev.. Agreed. Though please see the question I posted in the other thread: now I am not very sure whether we'll be able to mark a page as device exclusive if that page has mapcount>1. > > We can optimize this into the various variants above, but logically > device exclusive stop existing during fork. Makes sense, I think that's indeed what this patch did at least for the COW case, so I think Alistair did address that comment. It's just that I think we need to drop the other !COW case (imho that should correspond to the changes in copy_nonpresent_pte()) in this patch to guarantee it. I also hope we don't make copy_pte_range() even more complicated just to do the lock_page() right, so we could fail the fork() if the lock is hard to take. -- Peter Xu