From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C6F62262D11; Mon, 24 Feb 2025 20:53:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740430398; cv=none; b=ciRR9OGiG0zdFbN237ktJUL4X6lBQ1E1OSdOJg2B7VcD/Y1cnLDBv7n+S3YWr6r87sVeyayYW54A5euSyATHo9oeFJiu8ZxJ52yTPZIwgcrGUpBu7Y21wrS/JUiNpvk3o+SLjZxa40eyLacBiGL6Mh6BvhTse9ToVlHRHES0N7Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740430398; c=relaxed/simple; bh=pREGhWg1kcj3syTH2EZjMgzcwFGBKmTgaY0Mxt8vcBk=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=q+OTpjeTbYy6GEOUXAEVoE8StWTLMvAUuPS3yFVI5qG6BJTMGzfEbPKE/QpAB3985SIjmrUprIKnUmqfgEQfUtSeHNNVyo7LtMyVrbxF6Yv2kbDaErM/nuZh5sA1NTg0h7SZw/kjS9yMPZYkGRnf33lMVZr0ILFJdxo+C9W+NbA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fyckZLa0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fyckZLa0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 239D9C4CED6; Mon, 24 Feb 2025 20:53:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740430396; bh=pREGhWg1kcj3syTH2EZjMgzcwFGBKmTgaY0Mxt8vcBk=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=fyckZLa0MhIBkOEp96YFckrMzMItxbfarxjlThBvHzF1sF/J0CFKnvNBp3FK5rDqV qCOI1UPi2Y2K3/62XbfxPTdwTTxm1VfJVHLoz+UuI59cDt8HyYHaMMS8BE1+tzYx/e dABMISnYyfMQrv8W5+6p6JWhfV8A9P/bQjC9ZHbNv8uLwVgdjepzG/FM6wLg9mBsc0 f/59WF5i2asjjpGrAb4623fte1gUsev2wdavllCS4G6YPnuOcYRfM8jgNkWsBGOtLd Z9tWabzTxe1nvPrId3CMtisrbuovE4uESNGIdlatzdBqIbpnAUVaqk51ufZ7VZ4/49 sAX6TBzdjC5Cg== Date: Mon, 24 Feb 2025 14:53:14 -0600 From: Bjorn Helgaas To: Niklas Schnelle Cc: Christoph Hellwig , Alexandra Winter , Alex Williamson , Gerd Bayer , Matthew Rosato , Jason Gunthorpe , Thorsten Winkler , Bjorn Helgaas , Julian Ruess , Halil Pasic , Christian Borntraeger , Sven Schnelle , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: [PATCH v6 0/3] vfio/pci: s390: Fix issues preventing VFIO_PCI_MMAP=y for s390 and enable it Message-ID: <20250224205314.GA478317@bhelgaas> Precedence: bulk X-Mailing-List: kvm@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: <20250214-vfio_pci_mmap-v6-0-6f300cb63a7e@linux.ibm.com> On Fri, Feb 14, 2025 at 02:10:51PM +0100, Niklas Schnelle wrote: > With the introduction of memory I/O (MIO) instructions enbaled in commit > 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions") s390 > gained support for direct user-space access to mapped PCI resources. > Even without those however user-space can access mapped PCI resources > via the s390 specific MMIO syscalls. There is thus nothing fundamentally > preventing s390 from supporting VFIO_PCI_MMAP, allowing user-space > drivers to access PCI resources without going through the pread() > interface. To actually enable VFIO_PCI_MMAP a few issues need fixing > however. > > Firstly the s390 MMIO syscalls do not cause a page fault when > follow_pte() fails due to the page not being present. This breaks > vfio-pci's mmap() handling which lazily maps on first access. > > Secondly on s390 there is a virtual PCI device called ISM which has > a few oddities. For one it claims to have a 256 TiB PCI BAR (not a typo) > which leads to any attempt to mmap() it fail with the following message: > > vmap allocation for size 281474976714752 failed: use vmalloc= to increase size > > Even if one tried to map this BAR only partially the mapping would not > be usable on systems with MIO support enabled. So just block mapping > BARs which don't fit between IOREMAP_START and IOREMAP_END. Solve this > by keeping the vfio-pci mmap() blocking behavior around for this > specific device via a PCI quirk and new pdev->non_mappable_bars > flag. > > As noted by Alex Williamson With mmap() enabled in vfio-pci it makes > sense to also enable HAVE_PCI_MMAP with the same restriction for pdev-> > non_mappable_bars. So this is added in patch 3 and I tested this with > another small test program. > > Note: > For your convenience the code is also available in the tagged > b4/vfio_pci_mmap branch on my git.kernel.org site below: > https://git.kernel.org/pub/scm/linux/kernel/git/niks/linux.git/ > > Thanks, > Niklas > > Link: https://lore.kernel.org/all/c5ba134a1d4f4465b5956027e6a4ea6f6beff969.camel@linux.ibm.com/ > Signed-off-by: Niklas Schnelle > --- > Changes in v6: > - Add a patch to also enable PCI resource mmap() via sysfs and proc > exlcluding pdev->non_mappable_bars devices (Alex Williamson) > - Added Acks > - Link to v5: https://lore.kernel.org/r/20250212-vfio_pci_mmap-v5-0-633ca5e056da@linux.ibm.com I think the series would be more readable if patch 2/3 included all the core changes (adding pci_dev.non_mappable_bars, the 3/3 pci-sysfs.c and proc.c changes to test it, and I suppose the similar vfio_pci_core.c change), and we moved all the s390 content from 2/3 to 3/3.