[PATCH V2 8/9] xentrace: Support for ARM platform

[Benjamin Sanda <ben.sanda@dornerworks.com>]

Modified p2m_lookup() to provide support for xentrace on the ARM
platform. Added check for DOMID_XEN which skips PFN to MFN
translation. DOMID_XEN is considered a PV guest on x86 (i.e MFN ==
GFN), but on ARM there is no such concept. Thus requests to DOMID_XEN
on ARM use a MFN address directly and do not need translation from
PFN.

Check added to determine read/write or read only page type when
requesting DOMID_XEN. This is  done by checking the u.inuse.type_info
parameter of the requested page. The page rw/ro  paddr_t type is then
set accordingly.

Signed-off-by: Benjamin Sanda <ben.sanda@dornerworks.com>

---
Changed since v1:
  * Added check to determine page rw/ro type to correctly set the
    paddr_t to p2m_ram_rw or p2m_ram_ro instead of assuming p2m_ram_rw
  * Corrected block comment format to conform to Xen coding standard
---
 xen/arch/arm/p2m.c | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index a2a9c4b..a99b670 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -227,11 +227,38 @@ paddr_t p2m_lookup(struct domain *d, paddr_t paddr, p2m_type_t *t)
 {
     paddr_t ret;
     struct p2m_domain *p2m = &d->arch.p2m;
+    struct page_info *page;
+    unsigned long mfn;
 
-    spin_lock(&p2m->lock);
-    ret = __p2m_lookup(d, paddr, t);
-    spin_unlock(&p2m->lock);
-
+    /*
+    * DOMID_XEN is considered a PV guest on x86 (i.e MFN == GFN), but
+    * on ARM there is no such concept. Thus requests to DOMID_XEN
+    * on ARM use a MFN address directly and do not need translation 
+    * from PFN.
+    */
+    if(DOMID_XEN != d->domain_id)
+    {
+        spin_lock(&p2m->lock);
+        ret = __p2m_lookup(d, paddr, t);
+        spin_unlock(&p2m->lock);
+    }
+    else
+    {
+        /* retrieve the page to determine read/write or read only mapping */
+        mfn = paddr >> PAGE_SHIFT;
+        if (mfn_valid(mfn))
+        {
+            page = mfn_to_page(mfn);
+            *t = (page->u.inuse.type_info == PGT_writable_page ? 
+                                p2m_ram_rw : p2m_ram_ro);
+        }
+        else
+        {
+            *t = p2m_invalid;
+        }
+        ret = paddr;
+    }
+    
     return ret;
 }
 
-- 
2.5.0


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