RE: [PATCH v1 7/8] vfio/type1: Add VFIO_IOMMU_CACHE_INVALIDATE

[Tian, Kevin]

> From: Auger Eric <eric.auger@xxxxxxxxxx>
> Sent: Thursday, April 16, 2020 8:43 PM
> 
> Hi Kevin,
> On 4/16/20 2:09 PM, Tian, Kevin wrote:
> >> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> >> Sent: Thursday, April 16, 2020 6:40 PM
> >>
> >> Hi Alex,
> >> Still have a direction question with you. Better get agreement with you
> >> before heading forward.
> >>
> >>> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> >>> Sent: Friday, April 3, 2020 11:35 PM
> >> [...]
> >>>>>> + *
> >>>>>> + * returns: 0 on success, -errno on failure.
> >>>>>> + */
> >>>>>> +struct vfio_iommu_type1_cache_invalidate {
> >>>>>> +	__u32   argsz;
> >>>>>> +	__u32   flags;
> >>>>>> +	struct	iommu_cache_invalidate_info cache_info;
> >>>>>> +};
> >>>>>> +#define VFIO_IOMMU_CACHE_INVALIDATE      _IO(VFIO_TYPE,
> >>> VFIO_BASE
> >>>>> + 24)
> >>>>>
> >>>>> The future extension capabilities of this ioctl worry me, I wonder if
> >>>>> we should do another data[] with flag defining that data as
> >> CACHE_INFO.
> >>>>
> >>>> Can you elaborate? Does it mean with this way we don't rely on iommu
> >>>> driver to provide version_to_size conversion and instead we just pass
> >>>> data[] to iommu driver for further audit?
> >>>
> >>> No, my concern is that this ioctl has a single function, strictly tied
> >>> to the iommu uapi.  If we replace cache_info with data[] then we can
> >>> define a flag to specify that data[] is struct
> >>> iommu_cache_invalidate_info, and if we need to, a different flag to
> >>> identify data[] as something else.  For example if we get stuck
> >>> expanding cache_info to meet new demands and develop a new uapi to
> >>> solve that, how would we expand this ioctl to support it rather than
> >>> also create a new ioctl?  There's also a trade-off in making the ioctl
> >>> usage more difficult for the user.  I'd still expect the vfio layer to
> >>> check the flag and interpret data[] as indicated by the flag rather
> >>> than just passing a blob of opaque data to the iommu layer though.
> >>> Thanks,
> >>
> >> Based on your comments about defining a single ioctl and a unified
> >> vfio structure (with a @data[] field) for pasid_alloc/free, bind/
> >> unbind_gpasid, cache_inv. After some offline trying, I think it would
> >> be good for bind/unbind_gpasid and cache_inv as both of them use the
> >> iommu uapi definition. While the pasid alloc/free operation doesn't.
> >> It would be weird to put all of them together. So pasid alloc/free
> >> may have a separate ioctl. It would look as below. Does this direction
> >> look good per your opinion?
> >>
> >> ioctl #22: VFIO_IOMMU_PASID_REQUEST
> >> /**
> >>   * @pasid: used to return the pasid alloc result when flags ==
> ALLOC_PASID
> >>   *         specify a pasid to be freed when flags == FREE_PASID
> >>   * @range: specify the allocation range when flags == ALLOC_PASID
> >>   */
> >> struct vfio_iommu_pasid_request {
> >> 	__u32	argsz;
> >> #define VFIO_IOMMU_ALLOC_PASID	(1 << 0)
> >> #define VFIO_IOMMU_FREE_PASID	(1 << 1)
> >> 	__u32	flags;
> >> 	__u32	pasid;
> >> 	struct {
> >> 		__u32	min;
> >> 		__u32	max;
> >> 	} range;
> >> };
> >>
> >> ioctl #23: VFIO_IOMMU_NESTING_OP
> >> struct vfio_iommu_type1_nesting_op {
> >> 	__u32	argsz;
> >> 	__u32	flags;
> >> 	__u32	op;
> >> 	__u8	data[];
> >> };
> >>
> >> /* Nesting Ops */
> >> #define VFIO_IOMMU_NESTING_OP_BIND_PGTBL        0
> >> #define VFIO_IOMMU_NESTING_OP_UNBIND_PGTBL      1
> >> #define VFIO_IOMMU_NESTING_OP_CACHE_INVLD       2
> >>
> >
> > Then why cannot we just put PASID into the header since the
> > majority of nested usage is associated with a pasid?
> >
> > ioctl #23: VFIO_IOMMU_NESTING_OP
> > struct vfio_iommu_type1_nesting_op {
> > 	__u32	argsz;
> > 	__u32	flags;
> > 	__u32	op;
> > 	__u32   pasid;
> > 	__u8	data[];
> > };
> >
> > In case of SMMUv2 which supports nested w/o PASID, this field can
> > be ignored for that specific case.
> On my side I would prefer keeping the pasid in the data[]. This is not
> always used.
> 
> For instance, in iommu_cache_invalidate_info/iommu_inv_pasid_info we
> devised flags to tell whether the PASID is used.
> 

But don't we include a PASID in both invalidate structures already?

struct iommu_inv_addr_info {
#define IOMMU_INV_ADDR_FLAGS_PASID      (1 << 0)
#define IOMMU_INV_ADDR_FLAGS_ARCHID     (1 << 1)
#define IOMMU_INV_ADDR_FLAGS_LEAF       (1 << 2)
        __u32   flags;
        __u32   archid;
        __u64   pasid;
        __u64   addr;
        __u64   granule_size;
        __u64   nb_granules;
};

struct iommu_inv_pasid_info {
#define IOMMU_INV_PASID_FLAGS_PASID     (1 << 0)
#define IOMMU_INV_PASID_FLAGS_ARCHID    (1 << 1)
        __u32   flags;
        __u32   archid;
        __u64   pasid;
};

then consolidating the pasid field into generic header doesn't
hurt. the specific handler still rely on flags to tell whether it
is used?

Thanks
Kevin