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=-6.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 2BA74C433F5 for ; Sat, 18 Sep 2021 08:39:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04B236124B for ; Sat, 18 Sep 2021 08:39:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236657AbhIRIkf (ORCPT ); Sat, 18 Sep 2021 04:40:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:37016 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236345AbhIRIke (ORCPT ); Sat, 18 Sep 2021 04:40:34 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 70B506124B; Sat, 18 Sep 2021 08:39:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1631954351; bh=I3OXBH6Jsft3MeFXXif2KAYrH0PL5mHvHWDLsrpF3p0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=a9hjTcoDC0ygV/THN5MB4kBvc1nnulxFRN2ENZlTd88T2ditC8k61LEK7nro1pcKy 58YoRM/lwtdqh8GyJ8qXWBf/3Vx0F85rmORFagsAOyvTiRfGxdRnqMcvWAcFYC1YKF 375MnAbUtdYufFWtwtFjnlbzHb6ShWIbS2AWBWorMK1G9X3G85uL7vshrzItTf70VH KTqdnkocRfkn3jy+f8FEJabg3VvC7uH3Jng6O9C4dPMmbmv18gCNn/jpIMEJRH7Dyi MKcdnMDQZoWAMPe1dUw+5D79OrlymmveofL+SMizg3O59N3058HbTxrnBCSp1x6q3B G5psP8Km2jW+A== Received: by mail-oo1-f42.google.com with SMTP id k20-20020a4ad114000000b0029133123994so4012936oor.4; Sat, 18 Sep 2021 01:39:11 -0700 (PDT) X-Gm-Message-State: AOAM530yNhgT/PGtBX4j6jqqBmEn98rlAaaf5lLpTWVl48iOjaUgdEmA TsTgsbNsWrjA9SzrobPZX/rlPSOJW0lmqTJYlJ4= X-Google-Smtp-Source: ABdhPJwhjcwUIBun9pdQA2AKk6/UkuNunTe3+nY6kMyQMkX2egUVkh/hJR0L43iF+/kZGTei1N8EB2+UDKBIhXdrDvg= X-Received: by 2002:a05:6820:1049:: with SMTP id x9mr4953726oot.40.1631954350758; Sat, 18 Sep 2021 01:39:10 -0700 (PDT) MIME-Version: 1.0 References: <20210912165309.98695-1-ogabbay@kernel.org> <20210914161218.GF3544071@ziepe.ca> <20210916131014.GK3544071@ziepe.ca> In-Reply-To: From: Oded Gabbay Date: Sat, 18 Sep 2021 11:38:42 +0300 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v6 0/2] Add p2p via dmabuf to habanalabs To: Jason Gunthorpe , Daniel Vetter Cc: "Linux-Kernel@Vger. Kernel. Org" , Greg Kroah-Hartman , =?UTF-8?Q?Christian_K=C3=B6nig?= , Gal Pressman , Yossi Leybovich , Maling list - DRI developers , linux-rdma , Linux Media Mailing List , Doug Ledford , Dave Airlie , Alex Deucher , Leon Romanovsky , Christoph Hellwig , amd-gfx list , "moderated list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Fri, Sep 17, 2021 at 3:30 PM Daniel Vetter wrote: > > On Thu, Sep 16, 2021 at 10:10:14AM -0300, Jason Gunthorpe wrote: > > On Thu, Sep 16, 2021 at 02:31:34PM +0200, Daniel Vetter wrote: > > > On Wed, Sep 15, 2021 at 10:45:36AM +0300, Oded Gabbay wrote: > > > > On Tue, Sep 14, 2021 at 7:12 PM Jason Gunthorpe wrote: > > > > > > > > > > On Tue, Sep 14, 2021 at 04:18:31PM +0200, Daniel Vetter wrote: > > > > > > On Sun, Sep 12, 2021 at 07:53:07PM +0300, Oded Gabbay wrote: > > > > > > > Hi, > > > > > > > Re-sending this patch-set following the release of our user-space TPC > > > > > > > compiler and runtime library. > > > > > > > > > > > > > > I would appreciate a review on this. > > > > > > > > > > > > I think the big open we have is the entire revoke discussions. Having the > > > > > > option to let dma-buf hang around which map to random local memory ranges, > > > > > > without clear ownership link and a way to kill it sounds bad to me. > > > > > > > > > > > > I think there's a few options: > > > > > > - We require revoke support. But I've heard rdma really doesn't like that, > > > > > > I guess because taking out an MR while holding the dma_resv_lock would > > > > > > be an inversion, so can't be done. Jason, can you recap what exactly the > > > > > > hold-up was again that makes this a no-go? > > > > > > > > > > RDMA HW can't do revoke. > > > > > > Like why? I'm assuming when the final open handle or whatever for that MR > > > is closed, you do clean up everything? Or does that MR still stick around > > > forever too? > > > > It is a combination of uAPI and HW specification. > > > > revoke here means you take a MR object and tell it to stop doing DMA > > without causing the MR object to be destructed. > > > > All the drivers can of course destruct the MR, but doing such a > > destruction without explicit synchronization with user space opens > > things up to a serious use-after potential that could be a security > > issue. > > > > When the open handle closes the userspace is synchronized with the > > kernel and we can destruct the HW objects safely. > > > > So, the special HW feature required is 'stop doing DMA but keep the > > object in an error state' which isn't really implemented, and doesn't > > extend very well to other object types beyond simple MRs. > > Yeah revoke without destroying the MR doesn't work, and it sounds like > revoke by destroying the MR just moves the can of worms around to another > place. > > > > 1. User A opens gaudi device, sets up dma-buf export > > > > > > 2. User A registers that with RDMA, or anything else that doesn't support > > > revoke. > > > > > > 3. User A closes gaudi device > > > > > > 4. User B opens gaudi device, assumes that it has full control over the > > > device and uploads some secrets, which happen to end up in the dma-buf > > > region user A set up > > > > I would expect this is blocked so long as the DMABUF exists - eg the > > DMABUF will hold a fget on the FD of #1 until the DMABUF is closed, so > > that #3 can't actually happen. > > > > > It's not mlocked memory, it's mlocked memory and I can exfiltrate > > > it. > > > > That's just bug, don't make buggy drivers :) > > Well yeah, but given that habanalabs hand rolled this I can't just check > for the usual things we have to enforce this in drm. And generally you can > just open chardevs arbitrarily, and multiple users fighting over each > another. The troubles only start when you have private state or memory > allocations of some kind attached to the struct file (instead of the > underlying device), or something else that requires device exclusivity. > There's no standard way to do that. > > Plus in many cases you really want revoke on top (can't get that here > unfortunately it seems), and the attempts to get towards a generic > revoke() just never went anywhere. So again it's all hand-rolled > per-subsystem. *insert lament about us not having done this through a > proper subsystem* > > Anyway it sounds like the code takes care of that. > -Daniel Daniel, Jason, Thanks for reviewing this code. Can I get an R-B / A-B from you for this patch-set ? Thanks, Oded