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=-1.1 required=3.0 tests=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 969A9C433E0 for ; Mon, 22 Jun 2020 11:46:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 729FC20716 for ; Mon, 22 Jun 2020 11:46:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="k8sCtVsI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727938AbgFVLqW (ORCPT ); Mon, 22 Jun 2020 07:46:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60100 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727836AbgFVLqU (ORCPT ); Mon, 22 Jun 2020 07:46:20 -0400 Received: from mail-qk1-x744.google.com (mail-qk1-x744.google.com [IPv6:2607:f8b0:4864:20::744]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 107E7C061796 for ; Mon, 22 Jun 2020 04:46:20 -0700 (PDT) Received: by mail-qk1-x744.google.com with SMTP id b4so15076898qkn.11 for ; Mon, 22 Jun 2020 04:46:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=NBKzXepzy68inRcMiAHpgcaZ+EYis2uiV6fI4xhZtmM=; b=k8sCtVsIXQZTIM44uTx5XoGTEDbrW/uXOY8fvY9Nd/4DXh4saPSxYGA0cCfUbnlyLl tHW4PMUz+IUIg6iJElEk/IVvMc03r9mZCDo7PkP58fQDAGJJHKTvWbHlwGlvSkCSJBE9 Ppej67LhjF9DHjvuE14BQiJBd6KnkgcnIxlNFcmKmCUHQqePe85Gy7qlE4M8VsBeHKUS yKX1U0jk0j5Ks8Y76HvcbvQtdxXTdUE006wQlY/5i2fjpanXsf+qNhaiup+oN8Qg8/ox /U6VE787P4r0dXZDbqERqe83AX626e55WkuKobSm/QiJ7uDeG7xH7wfc6SCv8Inqo2Uq QFhA== 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=NBKzXepzy68inRcMiAHpgcaZ+EYis2uiV6fI4xhZtmM=; b=rmkvygbLYjaMJLXpPAEwlrdkTv2fHa/thIlji6pTb8hofhS423V413rpStIxwHJNHY /GOpWbmoRWGC0sPODKL/XMMmqjO6bEAts5U/XCo01f2gn+kqXS4XmHV0RNccBv839TSh oDVdUkX0VFbmyvSmhLwgV+U51PoXhgZ84V3Nr6wErHuYFQEhUOqoxAPdM1AToZOtW2Zp enF8cp2hzmC3T2LIVTtAJFQAfGLnZ1qO0gE+M3R87Ss4FEFKOLsII1cdW/fnvgf2NKC7 iuAvbZnBs8b0NG4NJ+kBfUhNt5N/UyjIff6ujRY+2+Nkzh1O48fmqEJb8qqJ56K9QgzY XYFw== X-Gm-Message-State: AOAM531IGBe672yJD2OMwl9EIbFfYCPPWjZzjO1CEca1tKbfnEMv0OrC RqTOt0XrDA6ZF/jWuio73Wb/ow== X-Google-Smtp-Source: ABdhPJxthYjyMVCe6ZAxMUNKsmIMBTQD1YPg4YWyLhscgW6iJ+jy7QK2ERT6it0ZxPEWrnvgAqzIOg== X-Received: by 2002:ae9:c00d:: with SMTP id u13mr15622504qkk.434.1592826379164; Mon, 22 Jun 2020 04:46:19 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-156-34-48-30.dhcp-dynamic.fibreop.ns.bellaliant.net. [156.34.48.30]) by smtp.gmail.com with ESMTPSA id r37sm14964604qtk.34.2020.06.22.04.46.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jun 2020 04:46:18 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.93) (envelope-from ) id 1jnKu1-00Brwt-CA; Mon, 22 Jun 2020 08:46:17 -0300 Date: Mon, 22 Jun 2020 08:46:17 -0300 From: Jason Gunthorpe To: Jerome Glisse Cc: Felix Kuehling , linux-rdma , Thomas =?utf-8?B?SGVsbHN0csO2bSAoSW50ZWwp?= , Maarten Lankhorst , LKML , DRI Development , Christian =?utf-8?B?S8O2bmln?= , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Thomas Hellstrom , amd-gfx list , Daniel Vetter , Daniel Vetter , Mika Kuoppala , Intel Graphics Development , "open list:DMA BUFFER SHARING FRAMEWORK" Subject: Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep annotations Message-ID: <20200622114617.GU6578@ziepe.ca> References: <20200619113934.GN6578@ziepe.ca> <20200619151551.GP6578@ziepe.ca> <20200619172308.GQ6578@ziepe.ca> <20200619180935.GA10009@redhat.com> <20200619181849.GR6578@ziepe.ca> <56008d64-772d-5757-6136-f20591ef71d2@amd.com> <20200619195538.GT6578@ziepe.ca> <20200619203147.GC13117@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200619203147.GC13117@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 19, 2020 at 04:31:47PM -0400, Jerome Glisse wrote: > Not doable as page refcount can change for things unrelated to GUP, with > John changes we can identify GUP and we could potentialy copy GUPed page > instead of COW but this can potentialy slow down fork() and i am not sure > how acceptable this would be. Also this does not solve GUP against page > that are already in fork tree ie page P0 is in process A which forks, > we now have page P0 in process A and B. Now we have process A which forks > again and we have page P0 in A, B, and C. Here B and C are two branches > with root in A. B and/or C can keep forking and grow the fork tree. For a long time now RDMA has broken COW pages when creating user DMA regions. The problem has been that fork re-COW's regions that had their COW broken. So, if you break the COW upon mapping and prevent fork (and others) from copying DMA pinned then you'd cover the cases. > Semantic was change with 17839856fd588f4ab6b789f482ed3ffd7c403e1f to some > what "fix" that but GUP fast is still succeptible to this. Ah, so everyone breaks the COW now, not just RDMA.. What do you mean 'GUP fast is still succeptible to this' ? Jason