Merge tag 'for-linus-5.17a-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen fixes from Juergen Gross:

 - documentation fixes related to Xen

 - enable x2apic mode when available when running as hardware
   virtualized guest under Xen

 - cleanup and fix a corner case of vcpu enumeration when running a
   paravirtualized Xen guest

* tag 'for-linus-5.17a-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  x86/Xen: streamline (and fix) PV CPU enumeration
  xen: update missing ioctl magic numers documentation
  Improve docs for IOCTL_GNTDEV_MAP_GRANT_REF
  xen: xenbus_dev.h: delete incorrect file name
  xen/x2apic: enable x2apic mode when supported for HVM

1 files changed, 7 insertions, 1 deletions

diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h
index 9ac5515b9bc2..7a7145395c09 100644
--- a/include/uapi/xen/gntdev.h
+++ b/include/uapi/xen/gntdev.h
@@ -47,7 +47,13 @@ struct ioctl_gntdev_grant_ref {
 /*
  * Inserts the grant references into the mapping table of an instance
  * of gntdev. N.B. This does not perform the mapping, which is deferred
- * until mmap() is called with @index as the offset.
+ * until mmap() is called with @index as the offset. @index should be
+ * considered opaque to userspace, with one exception: if no grant
+ * references have ever been inserted into the mapping table of this
+ * instance, @index will be set to 0. This is necessary to use gntdev
+ * with userspace APIs that expect a file descriptor that can be
+ * mmap()'d at offset 0, such as Wayland. If @count is set to 0, this
+ * ioctl will fail.
  */
 #define IOCTL_GNTDEV_MAP_GRANT_REF \
 _IOC(_IOC_NONE, 'G', 0, sizeof(struct ioctl_gntdev_map_grant_ref))