From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qt1-f178.google.com (mail-qt1-f178.google.com [209.85.160.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 928333EC686 for ; Mon, 12 Oct 2026 14:46:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791816381; cv=none; b=giwmkAN1w0gzOlR9Pb2l3HLkGf5zUv8azmkVjoWMRsNQnSkvnwErpGNZME6SxefOgTChCINVU1lgaevIipXeZ7TWgmCdvsmEs+0z3RdjL2j4upltRO/lhS5qgBnGS9Fqxqb8DJN7bhoHBTzgsj5juEtbfs9IqPqz+mtFmJwIv0E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791816381; c=relaxed/simple; bh=YarLj6Tl5drs4d48GxIIPRySQhK4PE3lDvu4dKT16oE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=igwWgk+udOmpJPWEXTVBxzhg5VYUlrM7GDKE1GA1d3i5wls261cKJuaGtMNPUyEpHtSpLeUX2FeGkHdqYQh2rU/xOMxFv7AB4GJl1SMuFiUbafiUr/tuxK1/0XEaApQnry8ZnglSxG1eGUyuIbuA22W2QfpihsHkX7gLcfrobM4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca; spf=pass smtp.mailfrom=ziepe.ca; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b=Z66BZ70G; arc=none smtp.client-ip=209.85.160.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ziepe.ca Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="Z66BZ70G" Received: by mail-qt1-f178.google.com with SMTP id d75a77b69052e-53440816851so21418541cf.0 for ; Mon, 12 Oct 2026 07:46:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1791816378; x=1792421178; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to:content-type; bh=kVDh4BcUbgvIW1O8+CoyCzwwqxHQNia8D9+ovujPztQ=; b=Z66BZ70GrL+G3fRSAa++wQ031ECfO0fS51Dh7ERYYOaggt42Ne8wL05RkyY1CINEJx dAH4bDpFvoxbV3Nbjo3T5t/TWrmGZHrIaHJ9rcDe6CzZ9JrhHdcdLybNTy1l+a5THPKR S8kXtrdBlOtRke0qkwgW0ZzCpt6Wqs/1kXrxSZcTNVeiBcEKEEZvvz/TgLuQTSihrHNf WBCQjBquZ+J0ZmdWo4+Qm1Nuj90rzq5A1TlecjN39HHMKV8Q0WhqMj1Bjf/7FOQjpsJC GuPr1dSttLysga5Bo4FH5pVFcvDbUY/9aZgigWdULgd+2dTZVipw3eKr12O3MtUUSavl 2fwg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791816378; x=1792421178; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=kVDh4BcUbgvIW1O8+CoyCzwwqxHQNia8D9+ovujPztQ=; b=vlAiRCRB/aYdtiaqOZW3O2YQxqS+wjFQnc+PhtpUCaGPIu4d5ahgqzWxazQMft+c13 tZ2gi+04qEQUGYYJI3yQ162elWAQ/xbWD/qj/J29HKaX1W4XSfo18E97SxoH9MMCZIa9 O6Iclyz/+efGiQ00n4K+bV4CrBegyYCS+RduT0atIB7xFJRvpd8Qm6O/WUfntJ1lRf0n I4sWSVUnDO2fY23QTeo52g4YkkxLHDOZv+jKWYDbYAgE46b01ZEVQ4u/7v8F4cnB6ahS O4mMuIyKHFj+qsoAHh1to/zFmFhFg0JfXeZYy5ZvlhuTllN75/M1B19oySwZyHKfjQId ibxQ== X-Forwarded-Encrypted: i=1; AKwUvBz4fRdNid+T7hL6N2FuS0YUjntxbh6pI2H7s6VdxIoRhZZnM8sep5DgQSf1upH3vroI9RXd5qUlznImAma4iNHU6ug=@vger.kernel.org X-Gm-Message-State: AFq9FYJoSbjMYApZkhigzF2k1G+1jxYs/FHt1SsJZdonNACzmXzqTC3G KDEpRZq2GitIsewkZV4B8p9mUfVrKVBXMRQNKPhygZX3ldUFYYDIdZFrK4+A8ij/ijo= X-Gm-Gg: AYBFou3Bm6P36jER43nszr2VT8d4Vu10VQkfzNUJIrU/EPe5QPBez6he5dOIVM8PDPz JyjXoqvg81/4kRuc3mdIftFkF16PXbjj65ngUitcsCa3D+elIg3j+LtFVpFM+rMdGN+Rs96zl1F Qfbg5eG+udAYe0Nh7MkgOSuVCn58kPjYSMEABNTOaGuxlpX7/BL6wSgvZJybz2CUP0r5/5++xLX NDkjSZGgUhbuqXKJkF/70/kBkh4bWieJiy4iA8K+TX1HAlrgp9K3dBkYTVah2mH7VURFW9C/JvK MCOU18hCmarRHYC/lfwgYxvKiv4v7yvjOxNKtHWaPGYImBDYdAWK9wlgaOXyRP+VOdo/Z7B7N1U n11zkImSKVDmkKxYi5VjUiOF6YkcDDJMnwVeS+YO04gundpQHE+YmlOV5wg/QB1JTSAsq/PJ8pr xttZMdI94WfEdWtGZ0l83r+IQ9WNieR8PCSSmuLV95woFu6iwGKEqJ5WTU0Bkc4ckUdaeKPShQ2 dO6cImgpDmTHL+wuuLRHosM3fh27b8STbAJ4Y/IaJzO51LzMDTkeUo1 X-Received: by 2002:a05:622a:2487:b0:535:1134:91b with SMTP id d75a77b69052e-5359faead4bmr160454661cf.14.1791816378499; Mon, 12 Oct 2026 07:46:18 -0700 (PDT) Received: from ziepe.ca (hlfxns010zw-159-2-239-150.pppoe-dynamic.high-speed.ns.bellaliant.net. [159.2.239.150]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-535e652f3c7sm3157041cf.26.2026.10.12.07.46.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Oct 2026 07:46:17 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1xGHI8-00000006SW2-2nlk; Mon, 12 Oct 2026 11:46:16 -0300 Date: Mon, 12 Oct 2026 11:46:16 -0300 From: Jason Gunthorpe To: Christian =?utf-8?B?S8O2bmln?= Cc: Fred Griffoul , Paolo Bonzini , Sean Christopherson , Marc Zyngier , Oliver Upton , Sumit Semwal , Kevin Tian , David Woodhouse , Ackerley Tng , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Steffen Eiden , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Joerg Roedel , Robin Murphy , Alex Williamson , Shuah Khan , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kselftest@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [RFC PATCH 2/6] dma-buf: Add get_phys() to describe a physical run Message-ID: <20261012144616.GF14213@ziepe.ca> References: <20261005132046.30025-1-griffoul@gmail.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Oct 05, 2026 at 04:53:34PM +0200, Christian König wrote: > > KVM gets its frames through the KVM-private guest_memfd provider > > interface from David's series. iommufd gets them through a private > > interface with the exporter, as it already does for vfio-pci. The new > > version adds a small registry in iommufd for that, which replaces the > > symbol_get() of the sample in David's series. The dma-buf is then only > > the handle and the existing revoke. > > Yeah that approach sounds totally sane to me. > > We have drivers which stuff all kind of resources, not just memory, > into a DMA-buf. That ranges from MMIO BARs to trigger FW operations > (doorbells) over full HW blocks (ordered appends, global wave sync > etc...) where two or more applications need to share which one is > used. > > That you then have a exporter private interface is for accessing > this is perfectly ok. > > The problem you are facing here is more that this is not limited to > one driver/module but multiple ones and you don't want module inter > dependencies because of the symbols. > > So symbol_get() is probably the right thing to do as long as we > don't have something like weak symbols or similar. I don't want to keep expanding this hack in iommufd. If dmabuf is to be used then dmabuf needs to provide a pluggable way to fill the iommu_domain that many exporters can plug into. I don't want to hardwire every exporter into iommufd, that makes no sense. The existing arrangement is to motivate solving this problem generically, not something to be expanded on. Jason