Hi Joerg, I sent out v10 with Randy's comments addressed but I didn't change this patch. Does my explanation below make sense? I am hoping to make it in v5.10 since many other pieces depend on it, your guidance is much appreciated.
Jacob On Fri, 18 Sep 2020 10:11:08 -0700, Jacob Pan <jacob.jun....@linux.intel.com> wrote: > Hi Joerg, > > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel <j...@8bytes.org> wrote: > > > On Fri, Sep 11, 2020 at 02:57:52PM -0700, Jacob Pan wrote: > > > There can be multiple vendor-specific PASID data formats used in UAPI > > > structures. This patch adds enum type with a last entry which makes > > > range checking much easier. > > > > But it also makes it much easier to screw up the numbers (which are ABI) > > by inserting a new value into the middle. I prefer defines here, or > > alternativly BUILD_BUG_ON() checks for the numbers. > > > I am not following, the purpose of IOMMU_PASID_FORMAT_LAST *is* for > preparing the future insertion of new value into the middle. > The checking against IOMMU_PASID_FORMAT_LAST is to protect ABI > compatibility by making sure that out of range format are rejected in all > versions of the ABI. > For example, in v5.10, ABI has IOMMU_PASID_FORMAT_LAST = 2, then user data > with format = 2 will be rejected. So this user app will not work or > released. > > Now say in v5.11, we add one more format in the middle and set > IOMMU_PASID_FORMAT_LAST = 3. Then user data with the new format = 2 can > be supported. > > Without the checking for IOMMU_PASID_FORMAT_LAST, at v5.10 time the user > binary may succeed and become legacy binary that we cannot break in v5.11. > This renders format = 2 unusable for v5.11. > > I thought enum makes it less susceptible to programming errors than > defines by making sure the ascending order. I might have missed your > point, could you elaborate? > > > Regards, > > > > Joerg > > > > > > > > Suggested-by: Alex Williamson <alex.william...@redhat.com> > > > Reviewed-by: Eric Auger <eric.au...@redhat.com> > > > Signed-off-by: Jacob Pan <jacob.jun....@linux.intel.com> > > > --- > > > include/uapi/linux/iommu.h | 8 ++++++-- > > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h > > > index b42acc8fe007..7cc6ee6c41f7 100644 > > > --- a/include/uapi/linux/iommu.h > > > +++ b/include/uapi/linux/iommu.h > > > @@ -298,11 +298,16 @@ struct iommu_gpasid_bind_data_vtd { > > > IOMMU_SVA_VTD_GPASID_PCD | > > > \ IOMMU_SVA_VTD_GPASID_PWT) > > > > > > +enum iommu_pasid_data_format { > > > + IOMMU_PASID_FORMAT_INTEL_VTD = 1, > > > + IOMMU_PASID_FORMAT_LAST, > > > +}; > > > + > > > /** > > > * struct iommu_gpasid_bind_data - Information about device and guest > > > PASID binding > > > * @argsz: User filled size of this data > > > * @version: Version of this data structure > > > - * @format: PASID table entry format > > > + * @format: PASID table entry format of enum > > > iommu_pasid_data_format type > > > * @flags: Additional information on guest bind request > > > * @gpgd: Guest page directory base of the guest mm to bind > > > * @hpasid: Process address space ID used for the guest mm in > > > host IOMMU @@ -321,7 +326,6 @@ struct iommu_gpasid_bind_data { > > > __u32 argsz; > > > #define IOMMU_GPASID_BIND_VERSION_1 1 > > > __u32 version; > > > -#define IOMMU_PASID_FORMAT_INTEL_VTD 1 > > > __u32 format; > > > __u32 addr_width; > > > #define IOMMU_SVA_GPASID_VAL (1 << 0) /* guest PASID valid */ > > > -- > > > 2.7.4 > > > Thanks, > > Jacob Thanks, Jacob