> From: Tian, Kevin <kevin.tian@xxxxxxxxx> > Sent: Thursday, April 27, 2023 2:42 PM > > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > > Sent: Wednesday, April 26, 2023 10:54 PM > > > > VFIO needs two reserved values. 0 is already reserved by initializing > > xarray with XA_FLAGS_ALLOC1. This reserves -1 by limiting the xa alloc > > range. > > > > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx> > > --- > > drivers/iommu/iommufd/main.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/iommu/iommufd/main.c > > b/drivers/iommu/iommufd/main.c > > index 3fbe636c3d8a..51b27c96c52f 100644 > > --- a/drivers/iommu/iommufd/main.c > > +++ b/drivers/iommu/iommufd/main.c > > @@ -28,6 +28,9 @@ struct iommufd_object_ops { > > static const struct iommufd_object_ops iommufd_object_ops[]; > > static struct miscdevice vfio_misc_dev; > > > > +/* -1 is reserved */ > > +#define iommufd_xa_limit_32b XA_LIMIT(0, (-2U)) > > + > > struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx, > > size_t size, > > enum iommufd_object_type type) > > @@ -50,7 +53,7 @@ struct iommufd_object *_iommufd_object_alloc(struct > > iommufd_ctx *ictx, > > * before calling iommufd_object_finalize(). > > */ > > rc = xa_alloc(&ictx->objects, &obj->id, XA_ZERO_ENTRY, > > - xa_limit_32b, GFP_KERNEL_ACCOUNT); > > + iommufd_xa_limit_32b, GFP_KERNEL_ACCOUNT); > > Just direct use XA_LIMIT() here. Ok. > btw do we need a contract so vfio can learn 0 and -1 are reserved or > fine to have a fixed assumption in later patches? I doubt how to do it. ☹ @Jason? What about your opinion? Regards, Yi Liu