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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 05B92C43381 for ; Wed, 3 Feb 2021 21:25:27 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5235264E4F for ; Wed, 3 Feb 2021 21:25:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5235264E4F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8F7156B0005; Wed, 3 Feb 2021 16:25:25 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8A8656B006C; Wed, 3 Feb 2021 16:25:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7BE0D6B006E; Wed, 3 Feb 2021 16:25:25 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0152.hostedemail.com [216.40.44.152]) by kanga.kvack.org (Postfix) with ESMTP id 66B9E6B0005 for ; Wed, 3 Feb 2021 16:25:25 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 28C9C180AD817 for ; Wed, 3 Feb 2021 21:25:25 +0000 (UTC) X-FDA: 77778237810.24.cow54_1412022275d6 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 0D6261A4A5 for ; Wed, 3 Feb 2021 21:25:25 +0000 (UTC) X-HE-Tag: cow54_1412022275d6 X-Filterd-Recvd-Size: 7694 Received: from mail-ot1-f45.google.com (mail-ot1-f45.google.com [209.85.210.45]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Wed, 3 Feb 2021 21:25:24 +0000 (UTC) Received: by mail-ot1-f45.google.com with SMTP id o12so1264805ote.12 for ; Wed, 03 Feb 2021 13:25:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=iZMC9aBcPlgaxRBYNOkc0uhviDBibZJkuU/B+Oy0jvs=; b=UfW064ti1wei0HSqGSWiNnLG6DFOWhizy1OMtq7YsgHPJUjNLJgQ3sD4Vfdo5jzZo6 ys04/M39ejGkJ1cVhVSxCIcJ1u6TVVTWmaejIGK/MXCRCkzyKQOpSte/rAMoBCaEAFVM 6FioN/ovomgPGZLBTDyHkuS4snoyUmUkC8rOs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=iZMC9aBcPlgaxRBYNOkc0uhviDBibZJkuU/B+Oy0jvs=; b=DIj1hAQGARYmzDtrFxntPW10rG5qDLTYrBIfC+U16uEV3xXPxc9xrLohYxfyHs/hH1 yNBZ87CSMh1AyK4CYLmmei1XCO/VuQ4N5Bp5vnSAtZ/tPaxfsBtShb5s0FJPt3y6ssur /cdYCtFwk6AnSMtfuYAxvaBWpHH2+TfR6posGp7zrmd1QCamJYU07NJ5Hne4dGIgduxU WPrvP7+jGXDXFdimboxwT867RNx1bseVfXLDByFvibObrZCuKSp6PSNpM7LVxPEnVs/t YJAky9bgpP0mYyMh0BsZ8PL6dr/KedEW0c4ABcNnK4SPDYgysIaOHqN1YK29LzqR/GGl 50TA== X-Gm-Message-State: AOAM530oV/GHL4A4xnkpo8mNJz/D9tQaKGnqBRRjBW2q43Ir9WHhhULz xnG7Q8GZoQjW8uQzoNxoDDbOOipgZKm2GmxMeLhICw== X-Google-Smtp-Source: ABdhPJyeyn1ayHYYRh5/JJcIY/+l0YzWXziRkV8RSQ+9BR+8vImNPQYSnTETeFgdBKs6kdQJIsa6PUWdvh/NnD62vdI= X-Received: by 2002:a9d:b85:: with SMTP id 5mr3433355oth.281.1612387523565; Wed, 03 Feb 2021 13:25:23 -0800 (PST) MIME-Version: 1.0 References: <20210203003134.2422308-1-surenb@google.com> <20210203015553.GX308988@casper.infradead.org> In-Reply-To: From: Daniel Vetter Date: Wed, 3 Feb 2021 22:25:11 +0100 Message-ID: Subject: Re: [Linaro-mm-sig] [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return of an error To: Suren Baghdasaryan Cc: Matthew Wilcox , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Sandeep Patil , =?UTF-8?Q?Christian_K=C3=B6nig?= , Android Kernel Team , James Jones , Linux Kernel Mailing List , Liam Mark , Brian Starkey , Christoph Hellwig , Minchan Kim , Linux MM , John Stultz , dri-devel , Chris Goldsworthy , Hridya Valsaraju , Andrew Morton , Robin Murphy , "open list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="UTF-8" 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 Wed, Feb 3, 2021 at 9:29 PM Daniel Vetter wrote: > > On Wed, Feb 3, 2021 at 9:20 PM Suren Baghdasaryan wrote: > > > > On Wed, Feb 3, 2021 at 12:52 AM Daniel Vetter wrote: > > > > > > On Wed, Feb 3, 2021 at 2:57 AM Matthew Wilcox wrote: > > > > > > > > On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote: > > > > > Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with > > > > > WARN_ON_ONCE and returning an error. This is to ensure users of the > > > > > vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage > > > > > and get an indication of an error without panicing the kernel. > > > > > This will help identifying drivers that need to clear VM_PFNMAP before > > > > > using dmabuf system heap which is moving to use vm_insert_page. > > > > > > > > NACK. > > > > > > > > The system may not _panic_, but it is clearly now _broken_. The device > > > > doesn't work, and so the system is useless. You haven't really improved > > > > anything here. Just bloated the kernel with yet another _ONCE variable > > > > that in a normal system will never ever ever be triggered. > > > > > > Also, what the heck are you doing with your drivers? dma-buf mmap must > > > call dma_buf_mmap(), even for forwarded/redirected mmaps from driver > > > char nodes. If that doesn't work we have some issues with the calling > > > contract for that function, not in vm_insert_page. > > > > The particular issue I observed (details were posted in > > https://lore.kernel.org/patchwork/patch/1372409) is that DRM drivers > > set VM_PFNMAP flag (via a call to drm_gem_mmap_obj) before calling > > dma_buf_mmap. Some drivers clear that flag but some don't. I could not > > find the answer to why VM_PFNMAP is required for dmabuf mappings and > > maybe someone can explain that here? > > If there is a reason to set this flag other than historical use of > > carveout memory then we wanted to catch such cases and fix the drivers > > that moved to using dmabuf heaps. However maybe there are other > > reasons and if so I would be very grateful if someone could explain > > them. That would help me to come up with a better solution. > > > > > Finally why exactly do we need to make this switch for system heap? > > > I've recently looked at gup usage by random drivers, and found a lot > > > of worrying things there. gup on dma-buf is really bad idea in > > > general. > > > > The reason for the switch is to be able to account dmabufs allocated > > using dmabuf heaps to the processes that map them. The next patch in > > this series https://lore.kernel.org/patchwork/patch/1374851 > > implementing the switch contains more details and there is an active > > discussion there. Would you mind joining that discussion to keep it in > > one place? > > How many semi-unrelated buffer accounting schemes does google come up with? > > We're at three with this one. > > And also we _cannot_ required that all dma-bufs are backed by struct > page, so requiring struct page to make this work is a no-go. > > Second, we do not want to all get_user_pages and friends to work on > dma-buf, it causes all kinds of pain. Yes on SoC where dma-buf are > exclusively in system memory you can maybe get away with this, but > dma-buf is supposed to work in more places than just Android SoCs. I just realized that vm_inser_page doesn't even work for CMA, it would upset get_user_pages pretty badly - you're trying to pin a page in ZONE_MOVEABLE but you can't move it because it's rather special. VM_SPECIAL is exactly meant to catch this stuff. -Daniel > If you want to account dma-bufs, and gpu memory in general, I'd say > the solid solution is cgroups. There's patches floating around. And > given that Google Android can't even agree internally on what exactly > you want I'd say we just need to cut over to that and make it happen. > > Cheers, Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch