On Wed, Sep 20, 2023 at 02:19:42PM +0200, Cédric Le Goater wrote: > On 9/20/23 05:42, Duan, Zhenzhong wrote: > > > > > > > -----Original Message----- > > > From: Cédric Le Goater <c...@redhat.com> > > > Sent: Wednesday, September 20, 2023 1:08 AM > > > Subject: Re: [PATCH v1 15/22] Add iommufd configure option > > > > > > On 8/30/23 12:37, Zhenzhong Duan wrote: > > > > This adds "--enable-iommufd/--disable-iommufd" to enable or disable > > > > iommufd support, enabled by default. > > > > > > Why would someone want to disable support at compile time ? It might > > > > For those users who only want to support legacy container feature? > > Let me know if you still prefer to drop this patch, I'm fine with that. > > I think it is too early. > > > > have been useful for dev but now QEMU should self-adjust at runtime > > > depending only on the host capabilities AFAIUI. Am I missing something ? > > > > IOMMUFD doesn't support all features of legacy container, so QEMU > > doesn't self-adjust at runtime by checking if host supports IOMMUFD. > > We need to specify it explicitly to use IOMMUFD as below: > > > > -object iommufd,id=iommufd0 > > -device vfio-pci,host=0000:02:00.0,iommufd=iommufd0 > > OK. I am not sure this is the correct interface yet. At first glance, > I wouldn't introduce a new object for a simple backend depending on a > kernel interface. I would tend to prefer a "iommu-something" property > of the vfio-pci device with string values: "legacy", "iommufd", "default" > and define the various interfaces (the ops you proposed) for each > depending on the user preference and the capabilities of the host and > possibly the device.
I think the idea came from Alex? The major point is to be able to have libvirt open /dev/iommufd and FD pass it into qemu and then share that single FD across all VFIOs. qemu will typically not be able to self-open /dev/iommufd as it is root-only. So the object is not exactly for the backend, the object is for the file descriptor. Adding a legacy/iommufd option to the vfio-pci device string doesn't address these needs. Jason
