Re: [PATCH 1/3] iommu/uapi: Define uapi version and capabilities

Jacob Pan
2020-02-06T18:17:32Z

On Thu, 6 Feb 2020 11:14:27 +0100
Auger Eric <eric.auger@redhat.com> wrote:

> Hi Jacob,
> On 1/29/20 7:02 AM, Jacob Pan wrote:
> > Define a unified UAPI version to be used for compatibility
> > checks between user and kernel.
> >
> > Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> > include/uapi/linux/iommu.h | 48
> > ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48
> > insertions(+)
> >
> > diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> > index fcafb6401430..65a26c2519ee 100644
> > --- a/include/uapi/linux/iommu.h
> > +++ b/include/uapi/linux/iommu.h
> > @@ -8,6 +8,54 @@
> >
> > #include <linux/types.h>
> >
> > +/**
> > + * Current version of the IOMMU user API. This is intended for
> > query
> > + * between user and kernel to determine compatible data structures.
> > + *
> > + * Having a single UAPI version to govern the user-kernel data
> > structures
> > + * makes compatibility check straightforward. On the contrary,
> > supporting
> > + * combinations of multiple versions of the data can be a
> > nightmare.
> I would rather put the above justification in the commit msg and not
> here.
make sense.

> > + *
> > + * UAPI version can be bumped up with the following rules:
> > + * 1. All data structures passed between user and kernel space
> > share
> > + * the same version number. i.e. any extension to to any
> > structure
> s/to to/to
will fix.

> > + * results in version bump up.
> in a version number increment?
sounds good, more specific.

> > + *
> > + * 2. Data structures are open to extension but closed to
> > modification.> + * New fields must be added at the end of each
> > data structure with
> > + * 64bit alignment. Flag bits can be added without size change
> > but
> > + * existing ones cannot be altered.
> > + *
> > + * 3. Versions are backward compatible.
> > + *
> > + * 4. Version to size lookup is supported by kernel internal API
> > for each
> > + * API function type. @version is mandatory for new data
> > structures
> > + * and must be at the beginning with type of __u32.
> > + */
> > +#define IOMMU_UAPI_VERSION 1
> > +static inline int iommu_get_uapi_version(void)
> > +{
> > + return IOMMU_UAPI_VERSION;
> > +}
> > +
> > +/*
> > + * Supported UAPI features that can be reported to user space.
> > + * These types represent the capability available in the kernel.
> > + *
> > + * REVISIT: UAPI version also implies the capabilities. Should we
> > + * report them explicitly?
> > + */
> > +enum IOMMU_UAPI_DATA_TYPES {
> > + IOMMU_UAPI_BIND_GPASID,
> > + IOMMU_UAPI_CACHE_INVAL,
> > + IOMMU_UAPI_PAGE_RESP,
> > + NR_IOMMU_UAPI_TYPE,
> > +};
> > +
> > +#define IOMMU_UAPI_CAP_MASK ((1 << IOMMU_UAPI_BIND_GPASID)
> > | \
> > + (1 << IOMMU_UAPI_CACHE_INVAL)
> > | \
> > + (1 << IOMMU_UAPI_PAGE_RESP))
> > +
> > #define IOMMU_FAULT_PERM_READ (1 << 0) /* read */
> > #define IOMMU_FAULT_PERM_WRITE (1 << 1) /* write */
> > #define IOMMU_FAULT_PERM_EXEC (1 << 2) /* exec */
> >
> Thanks
>
> Eric
>