linux-kernel - RE: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID

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Date:   Tue, 7 Apr 2020 04:52:21 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
CC:     "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Sun, Yi Y" <yi.y.sun@...el.com>, "Wu, Hao" <hao.wu@...el.com>
Subject: RE: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

> From: Alex Williamson
> Sent: Saturday, April 4, 2020 1:50 AM
[...]
> > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > > index 9e843a1..298ac80 100644
> > > > --- a/include/uapi/linux/vfio.h
> > > > +++ b/include/uapi/linux/vfio.h
> > > > @@ -794,6 +794,47 @@ struct vfio_iommu_type1_dma_unmap {
> > > >  #define VFIO_IOMMU_ENABLE	_IO(VFIO_TYPE, VFIO_BASE + 15)
> > > >  #define VFIO_IOMMU_DISABLE	_IO(VFIO_TYPE, VFIO_BASE + 16)
> > > >
> > > > +/*
> > > > + * PASID (Process Address Space ID) is a PCIe concept which
> > > > + * has been extended to support DMA isolation in fine-grain.
> > > > + * With device assigned to user space (e.g. VMs), PASID alloc
> > > > + * and free need to be system wide. This structure defines
> > > > + * the info for pasid alloc/free between user space and kernel
> > > > + * space.
> > > > + *
> > > > + * @flag=VFIO_IOMMU_PASID_ALLOC, refer to the @alloc_pasid
> > > > + * @flag=VFIO_IOMMU_PASID_FREE, refer to @free_pasid
> > > > + */
> > > > +struct vfio_iommu_type1_pasid_request {
> > > > +	__u32	argsz;
> > > > +#define VFIO_IOMMU_PASID_ALLOC	(1 << 0)
> > > > +#define VFIO_IOMMU_PASID_FREE	(1 << 1)
> > > > +	__u32	flags;
> > > > +	union {
> > > > +		struct {
> > > > +			__u32 min;
> > > > +			__u32 max;
> > > > +			__u32 result;
> > > > +		} alloc_pasid;
> > > > +		__u32 free_pasid;
> > > > +	};
> > >
> > > We seem to be using __u8 data[] lately where the struct at data is
> > > defined by the flags.  should we do that here?
> >
> > yeah, I can do that. BTW. Do you want to let the structure in the
> > lately patch share the same structure with this one? As I can foresee,
> > the two structures would look like similar as both of them include
> > argsz, flags and data[] fields. The difference is the definition of
> > flags. what about your opinion?
> >
> > struct vfio_iommu_type1_pasid_request {
> > 	__u32	argsz;
> > #define VFIO_IOMMU_PASID_ALLOC	(1 << 0)
> > #define VFIO_IOMMU_PASID_FREE	(1 << 1)
> > 	__u32	flags;
> > 	__u8	data[];
> > };
> >
> > struct vfio_iommu_type1_bind {
> >         __u32           argsz;
> >         __u32           flags;
> > #define VFIO_IOMMU_BIND_GUEST_PGTBL     (1 << 0)
> > #define VFIO_IOMMU_UNBIND_GUEST_PGTBL   (1 << 1)
> >         __u8            data[];
> > };
> 
> 
> Yes, I was even wondering the same for the cache invalidate ioctl, or
> whether this is going too far for a general purpose "everything related
> to PASIDs" ioctl.  We need to factor usability into the equation too.
> I'd be interested in opinions from others here too.  Clearly I don't
> like single use, throw-away ioctls, but I can find myself on either
> side of the argument that allocation, binding, and invalidating are all
> within the domain of PASIDs and could fall within a single ioctl or
> they each represent different facets of managing PASIDs and should have
> separate ioctls.  Thanks,
> 

Looking at uapi/linux/iommu.h:

* Invalidations by %IOMMU_INV_GRANU_DOMAIN don't take any argument other than
 * @version and @cache.

Although intel-iommu handles only PASID-related invalidation now, I
suppose other vendors (or future usages?) may allow non-pasid
based invalidation too based on above comment. 

Thanks
Kevin