iommufd: Reserve all negative IDs in the iommufd xarray

With this reservation, IOMMUFD users can encode the negative IDs for
specific purposes. e.g. VFIO needs two reserved values to tell userspace
the ID returned is not valid but has other meaning.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Tested-by: Terrence Xu <terrence.xu@intel.com>
Tested-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20230718105542.4138-4-yi.l.liu@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 3fbe636c3d8a694d692a6bb0c449482063765646..32ce7befc8ddfef7c8bddd99e3ee29f66ddbd21c 100644 (file)
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -50,7 +50,7 @@ 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);
+                     xa_limit_31b, GFP_KERNEL_ACCOUNT);
        if (rc)
                goto out_free;
        return obj;