[Xen-devel] [PATCH 06/22] Add support for copy only (sub-page) grants. These are like normal access grants, except:

[<steven.smith@xxxxxxxxxx>]

-- They can't be used to map the page (so can only be used in a
   GNTTABOP_copy hypercall).
-- It's possible to grant access with a finer granularity than whole
   pages.
-- Xen guarantees that they can be revoked quickly (a normal map
   grant can only be revoked with the cooperation of the domain which
   has been granted access).

Signed-off-by: Steven Smith <steven.smith@xxxxxxxxxx>
---
 drivers/xen/core/gnttab.c |   38 ++++++++++++++++++++++++++++++++++++++
 include/xen/gnttab.h      |   16 ++++++++++++++++
 2 files changed, 54 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/core/gnttab.c b/drivers/xen/core/gnttab.c
index 5484e7e..b32dd5d 100644
--- a/drivers/xen/core/gnttab.c
+++ b/drivers/xen/core/gnttab.c
@@ -198,6 +198,44 @@ void gnttab_grant_foreign_access_ref(grant_ref_t ref, 
domid_t domid,
 }
 EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref);
 
+int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
+                                       int flags, unsigned page_off,
+                                       unsigned length)
+{
+       int ref;
+
+       if (unlikely((ref = get_free_entry()) < 0))
+               return -ENOSPC;
+
+       gnttab_grant_foreign_access_ref_subpage(ref, domid, frame, flags,
+                                               page_off, length);
+
+       return ref;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_subpage);
+
+void gnttab_grant_foreign_access_ref_subpage(grant_ref_t ref, domid_t domid,
+                                            unsigned long frame, int flags,
+                                            unsigned page_off,
+                                            unsigned length)
+{
+       BUG_ON(flags & (GTF_accept_transfer | GTF_reading |
+                       GTF_writing | GTF_sub_page | GTF_permit_access));
+       BUG_ON(grant_table_version == 1);
+       shared.v2[ref].sub_page.frame = frame;
+       shared.v2[ref].sub_page.page_off = page_off;
+       shared.v2[ref].sub_page.length = length;
+       shared.v2[ref].hdr.domid = domid;
+       wmb();
+       shared.v2[ref].hdr.flags = GTF_permit_access | GTF_sub_page | flags;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref_subpage);
+
+int gnttab_subpage_grants_available(void)
+{
+       return grant_table_version == 2;
+}
+EXPORT_SYMBOL_GPL(gnttab_subpage_grants_available);
 
 int gnttab_query_foreign_access(grant_ref_t ref)
 {
diff --git a/include/xen/gnttab.h b/include/xen/gnttab.h
index bde65fd..90201da 100644
--- a/include/xen/gnttab.h
+++ b/include/xen/gnttab.h
@@ -54,6 +54,18 @@ struct gnttab_free_callback {
 int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
                                int flags);
 
+int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
+                                       int flags, unsigned page_off,
+                                       unsigned length);
+
+
+/*
+ * Are sub-page grants available on this version of Xen?  Returns 1 if
+ * they are, and 0 if they're not.
+ */
+int gnttab_subpage_grants_available(void);
+
+
 /*
  * End access through the given grant reference, iff the grant entry is no
  * longer in use.  Return 1 if the grant entry was freed, 0 if it is still in
@@ -98,6 +110,10 @@ void gnttab_cancel_free_callback(struct 
gnttab_free_callback *callback);
 
 void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
                                     unsigned long frame, int flags);
+void gnttab_grant_foreign_access_ref_subpage(grant_ref_t ref, domid_t domid,
+                                            unsigned long frame, int flags,
+                                            unsigned page_off,
+                                            unsigned length);
 
 void gnttab_grant_foreign_transfer_ref(grant_ref_t, domid_t domid,
                                       unsigned long pfn);
-- 
1.6.3.1


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