From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42046 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404191AbfITPx5 (ORCPT ); Fri, 20 Sep 2019 11:53:57 -0400 Subject: Re: [PATCH v4 4/4] vfio: pci: Using a device region to retrieve zPCI information References: <1567815231-17940-1-git-send-email-mjrosato@linux.ibm.com> <1567815231-17940-5-git-send-email-mjrosato@linux.ibm.com> <20190919172505.2eb075f8.cohuck@redhat.com> <20190920162607.16198c92.cohuck@redhat.com> From: Matthew Rosato Message-ID: Date: Fri, 20 Sep 2019 11:53:41 -0400 MIME-Version: 1.0 In-Reply-To: <20190920162607.16198c92.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Cornelia Huck Cc: sebott@linux.ibm.com, gerald.schaefer@de.ibm.com, pasic@linux.ibm.com, borntraeger@de.ibm.com, walling@linux.ibm.com, linux-s390@vger.kernel.org, iommu@lists.linux-foundation.org, joro@8bytes.org, linux-kernel@vger.kernel.org, alex.williamson@redhat.com, kvm@vger.kernel.org, heiko.carstens@de.ibm.com, robin.murphy@arm.com, gor@linux.ibm.com, pmorel@linux.ibm.com On 9/20/19 10:26 AM, Cornelia Huck wrote: > On Thu, 19 Sep 2019 16:57:10 -0400 > Matthew Rosato wrote: > >> On 9/19/19 11:25 AM, Cornelia Huck wrote: >>> On Fri, 6 Sep 2019 20:13:51 -0400 >>> Matthew Rosato wrote: >>> >>>> From: Pierre Morel >>>> >>>> We define a new configuration entry for VFIO/PCI, VFIO_PCI_ZDEV >>>> >>>> When the VFIO_PCI_ZDEV feature is configured we initialize >>>> a new device region, VFIO_REGION_SUBTYPE_ZDEV_CLP, to hold >>>> the information from the ZPCI device the use >>>> >>>> Signed-off-by: Pierre Morel >>>> Signed-off-by: Matthew Rosato >>>> --- >>>> drivers/vfio/pci/Kconfig | 7 +++ >>>> drivers/vfio/pci/Makefile | 1 + >>>> drivers/vfio/pci/vfio_pci.c | 9 ++++ >>>> drivers/vfio/pci/vfio_pci_private.h | 10 +++++ >>>> drivers/vfio/pci/vfio_pci_zdev.c | 85 +++++++++++++++++++++++++++++++++++++ >>>> 5 files changed, 112 insertions(+) >>>> create mode 100644 drivers/vfio/pci/vfio_pci_zdev.c >>>> >>>> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig >>>> index ac3c1dd..d4562a8 100644 >>>> --- a/drivers/vfio/pci/Kconfig >>>> +++ b/drivers/vfio/pci/Kconfig >>>> @@ -45,3 +45,10 @@ config VFIO_PCI_NVLINK2 >>>> depends on VFIO_PCI && PPC_POWERNV >>>> help >>>> VFIO PCI support for P9 Witherspoon machine with NVIDIA V100 GPUs >>>> + >>>> +config VFIO_PCI_ZDEV >>>> + bool "VFIO PCI Generic for ZPCI devices" >>>> + depends on VFIO_PCI && S390 >>>> + default y >>>> + help >>>> + VFIO PCI support for S390 Z-PCI devices >>> >>> >From that description, I'd have no idea whether I'd want that or not. >>> Is there any downside to enabling it? >>> >> >> :) Not really, you're just getting information from the hardware vs >> using hard-coded defaults. The only reason I could think of to turn it >> off would be if you wanted/needed to restore this hard-coded behavior. > > I'm not really sure whether that's worth adding a Kconfig switch for. > Won't older versions simply ignore the new region anyway? > Yes, you have a point here... This switch showed up in v3 of this series when Pierre changed to using a region to pass this info and I haven't yet found a 'why' he decided to add the Kconfig switch. If I can't convince myself of a reason to keep it, I'll just remove it from the next version. > Also, I don't think we have any migration compatibility issues, as > vfio-pci devices are not (yet) migrateable anyway. > >> >> bool "VFIO PCI support for generic ZPCI devices" ? > > "Support zPCI-specific configuration for VFIO PCI" ? > >> >> "Support for sharing ZPCI hardware device information between the host >> and guests." ? > > "Enabling this options exposes a region containing hardware > configuration for zPCI devices. This enables userspace (e.g. QEMU) to > supply proper configuration values instead of hard-coded defaults for > zPCI devices passed through via VFIO on s390. > > Say Y here." > > ? > Your descriptions are much better - thanks for the feedback!