> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > Sent: Tuesday, February 4, 2020 2:01 AM > To: Liu, Yi L <yi.l.liu@xxxxxxxxx> > Subject: Re: [RFC v3 4/8] vfio/type1: Add > VFIO_NESTING_GET_IOMMU_UAPI_VERSION > > On Fri, 31 Jan 2020 13:04:11 +0000 > "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote: > > > Hi Alex, > > > > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > > Sent: Thursday, January 30, 2020 7:57 AM > > > To: Liu, Yi L <yi.l.liu@xxxxxxxxx> > > > Subject: Re: [RFC v3 4/8] vfio/type1: Add > > > VFIO_NESTING_GET_IOMMU_UAPI_VERSION > > > > > > On Wed, 29 Jan 2020 04:11:48 -0800 > > > "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote: > > > > > > > From: Liu Yi L <yi.l.liu@xxxxxxxxx> > > > > > > > > In Linux Kernel, the IOMMU nesting translation (a.k.a. IOMMU dual stage > > > > translation capability) is abstracted in uapi/iommu.h, in which the uAPIs > > > > like bind_gpasid/iommu_cache_invalidate/fault_report/pgreq_resp are defined. > > > > > > > > VFIO_TYPE1_NESTING_IOMMU stands for the vfio iommu type which is backed > by > > > > IOMMU nesting translation capability. VFIO exposes the nesting capability > > > > to userspace and also exposes uAPIs (will be added in later patches) to user > > > > space for setting up nesting translation from userspace. Thus applications > > > > like QEMU could support vIOMMU for pass-through devices with IOMMU > nesting > > > > translation capability. > > > > > > > > As VFIO expose the nesting IOMMU programming to userspace, it also needs to > > > > provide an API for the uapi/iommu.h version check to ensure compatibility. > > > > This patch reports the iommu uapi version to userspace. Applications could > > > > use this API to do version check before further using the nesting uAPIs. > > > > > > > > Cc: Kevin Tian <kevin.tian@xxxxxxxxx> > > > > CC: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> > > > > Cc: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > > Cc: Eric Auger <eric.auger@xxxxxxxxxx> > > > > Cc: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx> > > > > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx> > > > > --- > > > > drivers/vfio/vfio.c | 3 +++ > > > > include/uapi/linux/vfio.h | 10 ++++++++++ > > > > 2 files changed, 13 insertions(+) > > > > > > > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > > > > index 425d60a..9087ad4 100644 > > > > --- a/drivers/vfio/vfio.c > > > > +++ b/drivers/vfio/vfio.c > > > > @@ -1170,6 +1170,9 @@ static long vfio_fops_unl_ioctl(struct file *filep, > > > > case VFIO_GET_API_VERSION: > > > > ret = VFIO_API_VERSION; > > > > break; > > > > + case VFIO_NESTING_GET_IOMMU_UAPI_VERSION: > > > > + ret = iommu_get_uapi_version(); > > > > + break; > > > > > > Shouldn't the type1 backend report this? It doesn't make much sense > > > that the spapr backend reports a version for something it doesn't > > > support. Better yet, provide this info gratuitously in the > > > VFIO_IOMMU_GET_INFO ioctl return like you do with nesting in the next > > > patch, then it can help the user figure out if this support is present. > > > > yeah, it would be better to report it by type1 backed. However, > > it is kind of issue when QEMU using it. > > > > My series "hooks" vSVA supports on VFIO_TYPE1_NESTING_IOMMU type. > > [RFC v3 09/25] vfio: check VFIO_TYPE1_NESTING_IOMMU support > > https://www.spinics.net/lists/kvm/msg205197.html > > > > In QEMU, it will determine the iommu type firstly and then invoke > > VFIO_SET_IOMMU. I think before selecting VFIO_TYPE1_NESTING_IOMMU, > > QEMU needs to check the IOMMU uAPI version. If IOMMU uAPI is incompatible, > > QEMU should not use VFIO_TYPE1_NESTING_IOMMU type. If > > VFIO_NESTING_GET_IOMMU_UAPI_VERSION is available after set iommu, then it > > may be an issue. That's why this series reports the version in vfio layer > > instead of type1 backend. > > Why wouldn't you use CHECK_EXTENSION? You could probe specifically for > a VFIO_TYP1_NESTING_IOMMU_UAPI_VERSION extension that returns the > version number. Thanks, oh, yes. Thanks for this guiding. :-) Regards, Yi Liu
