[Xen-devel] [PATCH v20 1/2] common: add a new mappable resource type: XENMEM_resource_grant_table

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

This patch allows grant table frames to be mapped using the
XENMEM_acquire_resource memory op.

NOTE: This patch expands the on-stack mfn_list array in acquire_resource()
      but it is still small enough to remain on-stack.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>

v19:
 - Add test to prevent PVH/HVM tools domains mapping grant status frames
   this way as the mapping infrastructure in Xen does not yet implement the
   necessary reference counting to make this safe.
 - Make sure grant table version is set before any attempt to grow the table.

v18:
 - Non-trivial re-base of grant table code.
 - Dropped Jan's R-b because of the grant table changes.

v13:
 - Re-work the internals to avoid using the XENMAPIDX_grant_table_status
   hack.

v12:
 - Dropped limit checks as requested by Jan.

v10:
 - Addressed comments from Jan.

v8:
 - The functionality was originally incorporated into the earlier patch
   "x86/mm: add HYPERVISOR_memory_op to acquire guest resources".
---
 xen/common/grant_table.c      | 74 +++++++++++++++++++++++++++++++++++--------
 xen/common/memory.c           | 56 +++++++++++++++++++++++++++++++-
 xen/include/public/memory.h   |  9 ++++--
 xen/include/xen/grant_table.h |  4 +++
 4 files changed, 127 insertions(+), 16 deletions(-)

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index d9ec711c73..9db8e953b3 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -3860,6 +3860,38 @@ int mem_sharing_gref_to_gfn(struct grant_table *gt, 
grant_ref_t ref,
 }
 #endif
 
+/* caller must hold read or write lock */
+static int gnttab_get_status_frame_mfn(struct domain *d,
+                                       unsigned long idx, mfn_t *mfn)
+{
+    struct grant_table *gt = d->grant_table;
+
+    if ( idx >= nr_status_frames(gt) )
+        return -EINVAL;
+
+    *mfn = _mfn(virt_to_mfn(gt->status[idx]));
+    return 0;
+}
+
+/* caller must hold write lock */
+static int gnttab_get_shared_frame_mfn(struct domain *d,
+                                       unsigned long idx, mfn_t *mfn)
+{
+    struct grant_table *gt = d->grant_table;
+
+    if ( gt->gt_version == 0 )
+        gt->gt_version = 1;
+
+    if ( (idx >= nr_grant_frames(gt)) && (idx < gt->max_grant_frames) )
+        gnttab_grow_table(d, idx + 1);
+
+    if ( idx >= nr_grant_frames(gt) )
+        return -EINVAL;
+
+    *mfn = _mfn(virt_to_mfn(gt->shared_raw[idx]));
+    return 0;
+}
+
 int gnttab_map_frame(struct domain *d, unsigned long idx, gfn_t gfn,
                      mfn_t *mfn)
 {
@@ -3877,21 +3909,11 @@ int gnttab_map_frame(struct domain *d, unsigned long 
idx, gfn_t gfn,
     {
         idx &= ~XENMAPIDX_grant_table_status;
         status = true;
-        if ( idx < nr_status_frames(gt) )
-            *mfn = _mfn(virt_to_mfn(gt->status[idx]));
-        else
-            rc = -EINVAL;
-    }
-    else
-    {
-        if ( (idx >= nr_grant_frames(gt)) && (idx < gt->max_grant_frames) )
-            gnttab_grow_table(d, idx + 1);
 
-        if ( idx < nr_grant_frames(gt) )
-            *mfn = _mfn(virt_to_mfn(gt->shared_raw[idx]));
-        else
-            rc = -EINVAL;
+        rc = gnttab_get_status_frame_mfn(d, idx, mfn);
     }
+    else
+        rc = gnttab_get_shared_frame_mfn(d, idx, mfn);
 
     if ( !rc && paging_mode_translate(d) &&
          !gfn_eq(gnttab_get_frame_gfn(gt, status, idx), INVALID_GFN) )
@@ -3906,6 +3928,32 @@ int gnttab_map_frame(struct domain *d, unsigned long 
idx, gfn_t gfn,
     return rc;
 }
 
+int gnttab_get_shared_frame(struct domain *d, unsigned long idx,
+                            mfn_t *mfn)
+{
+    struct grant_table *gt = d->grant_table;
+    int rc;
+
+    grant_write_lock(gt);
+    rc = gnttab_get_shared_frame_mfn(d, idx, mfn);
+    grant_write_unlock(gt);
+
+    return rc;
+}
+
+int gnttab_get_status_frame(struct domain *d, unsigned long idx,
+                            mfn_t *mfn)
+{
+    struct grant_table *gt = d->grant_table;
+    int rc;
+
+    grant_read_lock(gt);
+    rc = gnttab_get_status_frame_mfn(d, idx, mfn);
+    grant_read_unlock(gt);
+
+    return rc;
+}
+
 static void gnttab_usage_print(struct domain *rd)
 {
     int first = 1;
diff --git a/xen/common/memory.c b/xen/common/memory.c
index e29d596727..7910bb16cc 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -23,6 +23,7 @@
 #include <xen/numa.h>
 #include <xen/mem_access.h>
 #include <xen/trace.h>
+#include <xen/grant_table.h>
 #include <asm/current.h>
 #include <asm/hardirq.h>
 #include <asm/p2m.h>
@@ -982,6 +983,54 @@ static long xatp_permission_check(struct domain *d, 
unsigned int space)
     return xsm_add_to_physmap(XSM_TARGET, current->domain, d);
 }
 
+static int acquire_grant_table(struct domain *d, unsigned int id,
+                               unsigned long frame,
+                               unsigned int nr_frames,
+                               xen_pfn_t mfn_list[])
+{
+    unsigned int i = nr_frames;
+
+    /*
+     * FIXME: It is not currently safe to map grant status frames if they
+     *        will be inserted into the caller's P2M, because these
+     *        insertions are not yet properly reference counted.
+     *        This restriction can be removed when appropriate reference
+     *        counting is added.
+     */
+    if ( paging_mode_translate(current->domain) &&
+         (id == XENMEM_resource_grant_table_id_status) )
+        return -EOPNOTSUPP;
+
+    /* Iterate backwards in case table needs to grow */
+    while ( i-- != 0 )
+    {
+        mfn_t mfn = INVALID_MFN;
+        int rc;
+
+        switch ( id )
+        {
+        case XENMEM_resource_grant_table_id_shared:
+            rc = gnttab_get_shared_frame(d, frame + i, &mfn);
+            break;
+
+        case XENMEM_resource_grant_table_id_status:
+            rc = gnttab_get_status_frame(d, frame + i, &mfn);
+            break;
+
+        default:
+            rc = -EINVAL;
+            break;
+        }
+
+        if ( rc )
+            return rc;
+
+        mfn_list[i] = mfn_x(mfn);
+    }
+
+    return 0;
+}
+
 static int acquire_resource(
     XEN_GUEST_HANDLE_PARAM(xen_mem_acquire_resource_t) arg)
 {
@@ -992,7 +1041,7 @@ static int acquire_resource(
      * moment since they are small, but if they need to grow in future
      * use-cases then per-CPU arrays or heap allocations may be required.
      */
-    xen_pfn_t mfn_list[2];
+    xen_pfn_t mfn_list[32];
     int rc;
 
     if ( copy_from_guest(&xmar, arg, 1) )
@@ -1027,6 +1076,11 @@ static int acquire_resource(
 
     switch ( xmar.type )
     {
+    case XENMEM_resource_grant_table:
+        rc = acquire_grant_table(d, xmar.id, xmar.frame, xmar.nr_frames,
+                                 mfn_list);
+        break;
+
     default:
         rc = arch_acquire_resource(d, xmar.type, xmar.id, xmar.frame,
                                    xmar.nr_frames, mfn_list, &xmar.flags);
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index bf2f81faae..1735a53916 100644
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -611,16 +611,21 @@ struct xen_mem_acquire_resource {
     uint16_t type;
 
 #define XENMEM_resource_ioreq_server 0
+#define XENMEM_resource_grant_table 1
 
     /*
      * IN - a type-specific resource identifier, which must be zero
      *      unless stated otherwise.
      *
      * type == XENMEM_resource_ioreq_server -> id == ioreq server id
+     * type == XENMEM_resource_grant_table -> id defined below
      */
     uint32_t id;
-    /*
-     * IN/OUT - As an IN parameter number of frames of the resource
+
+#define XENMEM_resource_grant_table_id_shared 0
+#define XENMEM_resource_grant_table_id_status 1
+
+    /* IN/OUT - As an IN parameter number of frames of the resource
      *          to be mapped. However, if the specified value is 0 and
      *          frame_list is NULL then this field will be set to the
      *          maximum value supported by the implementation on return.
diff --git a/xen/include/xen/grant_table.h b/xen/include/xen/grant_table.h
index 0286ba33dd..c881414e5b 100644
--- a/xen/include/xen/grant_table.h
+++ b/xen/include/xen/grant_table.h
@@ -58,6 +58,10 @@ int mem_sharing_gref_to_gfn(struct grant_table *gt, 
grant_ref_t ref,
 
 int gnttab_map_frame(struct domain *d, unsigned long idx, gfn_t gfn,
                      mfn_t *mfn);
+int gnttab_get_shared_frame(struct domain *d, unsigned long idx,
+                            mfn_t *mfn);
+int gnttab_get_status_frame(struct domain *d, unsigned long idx,
+                            mfn_t *mfn);
 
 unsigned int gnttab_dom0_frames(void);
 
-- 
2.11.0


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