Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
Hi Joerg, On Thu, 24 Sep 2020 10:40:16 +0200, Joerg Roedel wrote: > > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel > > 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. > > But with the enum you could have: > > enum { > VTD_FOO, > SMMU_FOO, > LAST, > }; > > which makes VTD_FOO==0 and SMMU_FOO==1, and when in the next version > someone adds: > > enum { > VTD_FOO, > VTD_BAR, > SMMU_FOO, > LAST, > }; > > then SMMU_FOO will become 2 and break ABI. So I'd like to have this > checked somewhere. Got your point, will change to defines. Thanks, Jacob ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
Hi Jacob, On Fri, Sep 18, 2020 at 10:11:08AM -0700, Jacob Pan wrote: > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel 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. But with the enum you could have: enum { VTD_FOO, SMMU_FOO, LAST, }; which makes VTD_FOO==0 and SMMU_FOO==1, and when in the next version someone adds: enum { VTD_FOO, VTD_BAR, SMMU_FOO, LAST, }; then SMMU_FOO will become 2 and break ABI. So I'd like to have this checked somewhere. Regards, Joerg ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
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 wrote: > Hi Joerg, > > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel 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 > > > Reviewed-by: Eric Auger > > > Signed-off-by: Jacob Pan > > > --- > > > 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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
Hi Joerg, On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel 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 > > Reviewed-by: Eric Auger > > Signed-off-by: Jacob Pan > > --- > > 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_11 > > __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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
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. Regards, Joerg > > Suggested-by: Alex Williamson > Reviewed-by: Eric Auger > Signed-off-by: Jacob Pan > --- > 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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
[PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format
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. Suggested-by: Alex Williamson Reviewed-by: Eric Auger Signed-off-by: Jacob Pan --- 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_11 __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 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu