From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qt1-f170.google.com (mail-qt1-f170.google.com [209.85.160.170]) (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 9045730DEA6 for ; Wed, 10 Jun 2026 16:28:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781108931; cv=none; b=Z68IgP+hYXI2o7yGpB6NNjbhbE5VltqTQXkO1JEFOtDdEdTWb4uWyPe8YmYLQV/620zp0RirxyOJHOVIeHHL7UyC5piErROtn7Y04yAcepvx09RHMxvJeCje3Hh2fGXZd/kdtivpKJbDwVMelFIV22TG9Ov1VgWkuu0q7olr0f0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781108931; c=relaxed/simple; bh=oNtJLGUkWCaRM3PrOBCSWnEFF8AV6QL1YRj/wcqe5Nk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=L1b/0P6Kf/VjOVDWN42xA8VEKYerEIMxDuJC6B4R19NuXL4zoJqi2XseH9QGhoAjuk7PyTKFGJ/+rsW7XiO+v8kTwICuGiK1JdTtth/sgJ1tYgWIKwOXW0w2T1tQ908O+v4XAyZKXZHAbhrooyuto147DJd6dZaNT9wKt/QxxBw= 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=HHqd+2Ox; arc=none smtp.client-ip=209.85.160.170 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="HHqd+2Ox" Received: by mail-qt1-f170.google.com with SMTP id d75a77b69052e-51776b4de37so54085591cf.1 for ; Wed, 10 Jun 2026 09:28:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1781108929; x=1781713729; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=oNtJLGUkWCaRM3PrOBCSWnEFF8AV6QL1YRj/wcqe5Nk=; b=HHqd+2Oxxgfstvd/wG7ueC47k9AaXG6HUc5jm1vsWWMzobtt2kxh0bE1kJobuLGFkn C4UkRIdfPNS+oDSPxCUfu2WzD63r6SmUCCiU9m+hRhDZEbGPJMpfzMa1F5+e1mZLqCRp g8TLpkzlMiZr+us2QE1wKo/uGSRpHRdPa4+4YeZ0uYgEigi8lVzd6IQWV8tnUUF7pLh3 h+xEpxrkrhBbvVUrY+hTXaSnD97UwE8QRtfrtBlVQ6WnImcz4jq61s89DyRtB8EqxNiA 9dZhEWoZNAhri5PzbUze1hF37Yz72zuQeoUV5/sEixNc0cIChevlf6TnLSCxaWjYLb6M oSfw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781108929; x=1781713729; h=in-reply-to:content-disposition: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; bh=oNtJLGUkWCaRM3PrOBCSWnEFF8AV6QL1YRj/wcqe5Nk=; b=UxXylVumSi6Q5delNivNS/M/hQULjJcRJoPFXOJia/v3lGiMDXeGwpVZHnAYhc5b9I jS87C1R+B10SMYhzk3OR2us6lmhY7s+j5Ik3LDNhwQHbE79OUH/vQN0ZggtqKqXJQGoC LtxdwQdrmqlhyGyvcl4Sdfy3MaFIKHN6e9+3B0/kMZb4FxOz976Thj0VJlshbUEChhmy BON009GvfIvFdHqF26r3D5ZhXb5V7TTCHZvYCbZ/3tbSLh2Gi942xunA/kRdUq0yriKk CZ6kB64muzb/siu7zZvPVBYOq/mRcx7MEMcUEHaD6qWZtlBmQ4aNYD2jfYFLKrCOjQJQ z9rw== X-Forwarded-Encrypted: i=1; AFNElJ+KGD8RHt9Rgm2K3iJJkmS7spRba+tSssp/V9tg7F2qtIZ1+PtXmRrZbpljORDL63gd52N4RHM2KQ76zps=@vger.kernel.org X-Gm-Message-State: AOJu0YxKf3MVCZ3SybW+A23j1GxL27+C29dfy6kthCp6zEYZjOCZ5gVP 68K/xu88cJ85hSCmwNSSPw7ixjtGUASOD+bG2i404Iz/Hid4/UZVuNdqf9n63RhTGOI= X-Gm-Gg: Acq92OGxTOrk+Kfbqwo6ipd5x3Z+b54tkxr+yHQoqIZCz1ypCqHNj4SHihG1fcPM4VF U7Bg/PW+94gmWE6tzMLuQgjCRNNH8vELrA8vLaeuGeHHrojDd5FX+IJZS3v+LBkUUNe1g617GAd doPudjNQx/iICt9XoYjOcFLhT7vvZg723KJVLLVr8OZnReJAII3iseU/HO9yQTe6/h3R5QTFUKK sTql7WVX270jBVmbFItDDScZboweQkvevyAYn8rVjSbtjqPA1vJxkD/CvY8xDx3cq7cyT+Q68e7 AWTOxbbQQIzalChfHrgJzEnTEjfn3GSxvMJgJWzJA/1kCANIdLKR4SF7fOTvLAUl7HwsHUOAtIy 9+dKh+2+ZT9g3kxrZTVIwiTIVdt5wRVALPHPTMsQl3JG3VARdmxdzGgfSJWPR/2oGrHTGb9JoD/ AkZspK1qCBs5KK7sWCtdrlEXInoAyFsrHzzCCfoDcAiZka810xtc+nDrjRVa19IZSe0pNbLjlSA AInMgzX7Ozcb1ms X-Received: by 2002:a05:622a:5b0a:b0:517:7faf:bafb with SMTP id d75a77b69052e-51795bfd7d2mr326551591cf.40.1781108929553; Wed, 10 Jun 2026 09:28:49 -0700 (PDT) Received: from ziepe.ca (crbknf0213w-47-54-130-67.pppoe-dynamic.high-speed.nl.bellaliant.net. [47.54.130.67]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-51775c60dedsm214392091cf.13.2026.06.10.09.28.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jun 2026 09:28:48 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wXLnM-000000047em-15sV; Wed, 10 Jun 2026 13:28:48 -0300 Date: Wed, 10 Jun 2026 13:28:48 -0300 From: Jason Gunthorpe To: Pranjal Shrivastava Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Bjorn Helgaas , Logan Gunthorpe , Alex Williamson , Kevin Tian , Ankit Agrawal , Matt Evans , Vivek Kasireddy , Leon Romanovsky , Shivaji Kant , Samiullah Khawaja Subject: Re: [RFC PATCH 0/5] vfio/pci: Support ZONE_DEVICE-backed P2P Registration Message-ID: <20260610162848.GO2764304@ziepe.ca> References: <20260610151853.3608948-1-praan@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260610151853.3608948-1-praan@google.com> On Wed, Jun 10, 2026 at 03:18:48PM +0000, Pranjal Shrivastava wrote: > Users utilize the standard sysfs p2pmem/allocate interface for managing > memory slices once a BAR is registered. I'm shocked someone wants to use API, what are you expecting to do with it?? > An alternative implementation has been explored which integrates with the > ongoing VFIO DMABUF-mmap refactor [1]. In that approach, rather than > registering a BAR as a system-wide P2P provider, VFIO optionally > allocates ZONE_DEVICE pages only for specifically exported DMABUFs via a > new VFIO_DMA_BUF_FLAG_ALLOC_STRUCT_PAGES flag. That's probably more sensible but you can't have a DMABUF mmap actually install non-special memory. The native vfio mmap still can, but not mmap on the dmabuf fd. That's still workable, just keep in mind. What do you even intend to do with this? With the new work to tie dmabuf directly into io_uring I really wonder if this is worth doing for VFIO? Jason