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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"mtosatti@redhat.com" <mtosatti@redhat.com>,
	"thomas@monjalon.net" <thomas@monjalon.net>,
	"bluca@debian.org" <bluca@debian.org>,
	"jerinjacobk@gmail.com" <jerinjacobk@gmail.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>,
	"cohuck@redhat.com" <cohuck@redhat.com>
Subject: Re: [dpdk-dev] [PATCH v2 5/7] vfio/pci: Add sriov_configure support
Date: Fri, 6 Mar 2020 07:57:19 +0000
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D19D7C07A0@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <20200305112230.0dd77712@w520.home>

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Friday, March 6, 2020 2:23 AM
> 
> On Tue, 25 Feb 2020 03:08:00 +0000
> "Tian, Kevin" <kevin.tian@intel.com> wrote:
> 
> > > From: Alex Williamson
> > > Sent: Thursday, February 20, 2020 2:54 AM
> > >
> > > With the VF Token interface we can now expect that a vfio userspace
> > > driver must be in collaboration with the PF driver, an unwitting
> > > userspace driver will not be able to get past the GET_DEVICE_FD step
> > > in accessing the device.  We can now move on to actually allowing
> > > SR-IOV to be enabled by vfio-pci on the PF.  Support for this is not
> > > enabled by default in this commit, but it does provide a module option
> > > for this to be enabled (enable_sriov=1).  Enabling VFs is rather
> > > straightforward, except we don't want to risk that a VF might get
> > > autoprobed and bound to other drivers, so a bus notifier is used to
> > > "capture" VFs to vfio-pci using the driver_override support.  We
> > > assume any later action to bind the device to other drivers is
> > > condoned by the system admin and allow it with a log warning.
> > >
> > > vfio-pci will disable SR-IOV on a PF before releasing the device,
> > > allowing a VF driver to be assured other drivers cannot take over the
> > > PF and that any other userspace driver must know the shared VF token.
> > > This support also does not provide a mechanism for the PF userspace
> > > driver itself to manipulate SR-IOV through the vfio API.  With this
> > > patch SR-IOV can only be enabled via the host sysfs interface and the
> > > PF driver user cannot create or remove VFs.
> >
> > I'm not sure how many devices can be properly configured simply
> > with pci_enable_sriov. It is not unusual to require PF driver prepare
> > something before turning PCI SR-IOV capability. If you look kernel
> > PF drivers, there are only two using generic pci_sriov_configure_
> > simple (simple wrapper like pci_enable_sriov), while most others
> > implementing their own callback. However vfio itself has no idea
> > thus I'm not sure how an user knows whether using this option can
> > actually meet his purpose. I may miss something here, possibly
> > using DPDK as an example will make it clearer.
> 
> There is still the entire vfio userspace driver interface.  Imagine for
> example that QEMU emulates the SR-IOV capability and makes a call out
> to libvirt (or maybe runs with privs for the PF SR-IOV sysfs attribs)
> when the guest enables SR-IOV.  Can't we assume that any PF specific
> support can still be performed in the userspace/guest driver, leaving
> us with a very simple and generic sriov_configure callback in vfio-pci?

Makes sense. One concern, though, is how an user could be warned
if he inadvertently uses sysfs to enable SR-IOV on a vfio device whose
userspace driver is incapable of handling it. Note any VFIO device, 
if SR-IOV capable, will allow user to do so once the module option is 
turned on and the callback is registered. I felt such uncertainty can be 
contained by toggling SR-IOV through a vfio api, but from your description 
obviously it is what you want to avoid. Is it due to the sequence reason,
e.g. that SR-IOV must be enabled before userspace PF driver sets the 
token? 

Thanks
Kevin

  parent reply	other threads:[~2020-03-09  8:59 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-19 18:53 [dpdk-dev] [PATCH v2 0/7] vfio/pci: SR-IOV support Alex Williamson
2020-02-19 18:53 ` [dpdk-dev] [PATCH v2 1/7] vfio: Include optional device match in vfio_device_ops callbacks Alex Williamson
2020-02-19 18:54 ` [dpdk-dev] [PATCH v2 2/7] vfio/pci: Implement match ops Alex Williamson
2020-02-19 18:54 ` [dpdk-dev] [PATCH v2 3/7] vfio/pci: Introduce VF token Alex Williamson
2020-02-25  2:59   ` Tian, Kevin
2020-03-05 18:17     ` Alex Williamson
2020-03-06  8:32       ` Tian, Kevin
2020-03-06 15:39         ` Alex Williamson
2020-03-07  1:04           ` Tian, Kevin
2020-03-09  0:46             ` Alex Williamson
2020-03-09  1:22               ` Tian, Kevin
2020-03-09  1:33               ` Tian, Kevin
2020-03-09 15:35                 ` Alex Williamson
2020-02-19 18:54 ` [dpdk-dev] [PATCH v2 4/7] vfio: Introduce VFIO_DEVICE_FEATURE ioctl and first user Alex Williamson
2020-02-27 17:34   ` Cornelia Huck
2020-03-05 20:51     ` Alex Williamson
2020-02-19 18:54 ` [dpdk-dev] [PATCH v2 5/7] vfio/pci: Add sriov_configure support Alex Williamson
2020-02-25  3:08   ` Tian, Kevin
2020-03-05 18:22     ` Alex Williamson
2020-03-05 20:08       ` Ajit Khaparde
2020-03-06  7:57       ` Tian, Kevin [this message]
2020-03-06 22:17         ` Alex Williamson
2020-03-07  1:35           ` Tian, Kevin
2020-03-09  0:46             ` Alex Williamson
2020-03-09  1:48               ` Tian, Kevin
2020-03-09 14:56                 ` Alex Williamson
2020-03-06  9:45       ` Tian, Kevin
2020-03-06 15:50         ` Alex Williamson
2020-02-19 18:54 ` [dpdk-dev] [PATCH v2 6/7] vfio/pci: Remove dev_fmt definition Alex Williamson
2020-02-19 18:54 ` [dpdk-dev] [PATCH v2 7/7] vfio/pci: Cleanup .probe() exit paths Alex Williamson
2020-02-25  2:33 ` [dpdk-dev] [PATCH v2 0/7] vfio/pci: SR-IOV support Tian, Kevin
2020-02-25  6:09   ` Jason Wang
2020-03-05 17:14     ` Alex Williamson
2020-03-06  3:35       ` Jason Wang
2020-03-06 16:24         ` Alex Williamson
2020-03-09  3:36           ` Jason Wang
2020-03-09 14:45             ` Alex Williamson
2020-03-05 17:33   ` Alex Williamson
2020-03-06  9:21     ` Tian, Kevin
2020-03-05  6:38 ` Vamsi Krishna Attunuru

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