Re: [RFC PATCH 7/8] VFIO: Add new IOCTL for IOMMU TLB invalidate propagation

["Liu, Yi L" <yi.l.liu@linux.intel.com>]

On Fri, May 12, 2017 at 03:58:43PM -0600, Alex Williamson wrote:
> On Wed, 26 Apr 2017 18:12:04 +0800
> "Liu, Yi L" <yi.l.liu@intel.com> wrote:
> 
> > From: "Liu, Yi L" <yi.l.liu@linux.intel.com>
> > 
> > This patch adds VFIO_IOMMU_TLB_INVALIDATE to propagate IOMMU TLB
> > invalidate request from guest to host.
> > 
> > In the case of SVM virtualization on VT-d, host IOMMU driver has
> > no knowledge of caching structure updates unless the guest
> > invalidation activities are passed down to the host. So a new
> > IOCTL is needed to propagate the guest cache invalidation through
> > VFIO.
> > 
> > Signed-off-by: Liu, Yi L <yi.l.liu@linux.intel.com>
> > ---
> >  include/uapi/linux/vfio.h | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 6b97987..50c51f8 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -564,6 +564,15 @@ struct vfio_device_svm {
> >  
> >  #define VFIO_IOMMU_SVM_BIND_TASK	_IO(VFIO_TYPE, VFIO_BASE + 22)
> >  
> > +/* For IOMMU TLB Invalidation Propagation */
> > +struct vfio_iommu_tlb_invalidate {
> > +	__u32	argsz;
> > +	__u32	length;
> > +	__u8	data[];
> > +};
> > +
> > +#define VFIO_IOMMU_TLB_INVALIDATE	_IO(VFIO_TYPE, VFIO_BASE + 23)
> 
> I'm kind of wondering why this isn't just a new flag bit on
> vfio_device_svm, the data structure is so similar.  Of course data
> needs to be fully specified in uapi.

Hi Alex,

For this part, it depends on using opaque structure or not. The following
link mentioned it in [Open] session.

http://www.spinics.net/lists/kvm/msg148798.html

If we pick the full opaque solution for iommu tlb invalidate propagation.
Then I may add a flag bit on vfio_device_svm and also add definition in
uapi as you suggested.

Thanks,
Yi L

> > +
> >  /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
> >  
> >  /*
>