[Xen-devel] [PATCH v2 2/2] xen/arm: introduce XENFEAT_grant_map_identity

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

The flag specifies that the hypervisor maps a grant page to guest
physical address == machine address of the page in addition to the
normal grant mapping address.

Frontends are allowed to map the same page multiple times using multiple
grant references. On the backend side it can be difficult to find out
the physical address corresponding to a particular machine address,
especially at the completation of a dma operation. To simplify address
translations, we introduce a second mapping of the grant at physical
address == machine address so that dom0 can issue cache maintenance
operations without having to find the pfn.

Call arch_grant_map_page_identity and arch_grant_unmap_page_identity
from __gnttab_map_grant_ref and __gnttab_unmap_common to introduce the
second mapping if the domain is directly mapped.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

---

Changes in v2:
- rename XENFEAT_grant_map_11 to XENFEAT_grant_map_identity;
- remove superfluous ifdef CONFIG_ARM in xen/common/kernel.c;
- don't modify gnttab_need_iommu_mapping;
- call arch_grant_map_page_identity and arch_grant_unmap_page_identity
from grant_table functions.
---
 xen/common/grant_table.c      |   35 +++++++++++++++++++++++++++--------
 xen/common/kernel.c           |    2 ++
 xen/include/public/features.h |    3 +++
 3 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 464007e..06cc88f 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -727,7 +727,7 @@ __gnttab_map_grant_ref(
 
     double_gt_lock(lgt, rgt);
 
-    if ( gnttab_need_iommu_mapping(ld) )
+    if ( gnttab_need_iommu_mapping(ld) || is_domain_direct_mapped(ld) )
     {
         unsigned int wrc, rdc;
         int err = 0;
@@ -738,13 +738,23 @@ __gnttab_map_grant_ref(
              !(old_pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) )
         {
             if ( wrc == 0 )
-                err = iommu_map_page(ld, frame, frame,
-                                     IOMMUF_readable|IOMMUF_writable);
+            {
+                if ( gnttab_need_iommu_mapping(ld) )
+                    err = iommu_map_page(ld, frame, frame,
+                            IOMMUF_readable|IOMMUF_writable);
+                else
+                    err = arch_grant_map_page_identity(ld, frame, true);
+            }
         }
         else if ( act_pin && !old_pin )
         {
             if ( (wrc + rdc) == 0 )
-                err = iommu_map_page(ld, frame, frame, IOMMUF_readable);
+            {
+                if ( gnttab_need_iommu_mapping(ld) )
+                    err = iommu_map_page(ld, frame, frame, IOMMUF_readable);
+                else
+                    err = arch_grant_map_page_identity(ld, frame, false);
+            }
         }
         if ( err )
         {
@@ -935,15 +945,24 @@ __gnttab_unmap_common(
             act->pin -= GNTPIN_hstw_inc;
     }
 
-    if ( gnttab_need_iommu_mapping(ld) )
+    if ( gnttab_need_iommu_mapping(ld) || is_domain_direct_mapped(ld) )
     {
         unsigned int wrc, rdc;
         int err = 0;
         mapcount(lgt, rd, op->frame, &wrc, &rdc);
         if ( (wrc + rdc) == 0 )
-            err = iommu_unmap_page(ld, op->frame);
-        else if ( wrc == 0 )
-            err = iommu_map_page(ld, op->frame, op->frame, IOMMUF_readable);
+        {
+            if ( gnttab_need_iommu_mapping(ld) )
+                err = iommu_unmap_page(ld, op->frame);
+            else
+                err = arch_grant_unmap_page_identity(ld, op->frame);
+        } else if ( wrc == 0 )
+        {
+            if ( gnttab_need_iommu_mapping(ld) )
+                err = iommu_map_page(ld, op->frame, op->frame, 
IOMMUF_readable);
+            else
+                err = arch_grant_map_page_identity(ld, op->frame, false);
+        }
         if ( err )
         {
             rc = GNTST_general_error;
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 7e83353..fa40a36 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -325,6 +325,8 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
                 break;
             }
 #endif
+            if ( is_domain_direct_mapped(d) )
+                fi.submap |= 1U << XENFEAT_grant_map_identity;
             break;
         default:
             return -EINVAL;
diff --git a/xen/include/public/features.h b/xen/include/public/features.h
index a149aa6..ba753a0 100644
--- a/xen/include/public/features.h
+++ b/xen/include/public/features.h
@@ -94,6 +94,9 @@
 /* operation as Dom0 is supported */
 #define XENFEAT_dom0                      11
 
+/* Xen also maps grant references at pfn = mfn */
+#define XENFEAT_grant_map_identity              12
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
-- 
1.7.10.4


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