From: Tim Deegan <Tim.Deegan@citrix.com>
Date: Thu, 5 May 2011 16:40:34 +0000 (+0100)
Subject: x86/mm: don't treat entirely empty p2m entries as RAM.
X-Git-Tag: 4.2.0-rc1~2283
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=31915b333f5413d3be1f9f90aace5bf8b3cedab0;p=xen.git

x86/mm: don't treat entirely empty p2m entries as RAM.

The AMD IOMMU pagetable-sharing code switched p2m type 0 to be
r/w RAM rather than invalid.  Be more careful when translating
from PTEs to p2m types that we don't treat all-zeros as a
RAM mapping of frame zero.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
---

diff --git a/xen/arch/x86/mm/hap/p2m-ept.c b/xen/arch/x86/mm/hap/p2m-ept.c
index f1c2b0ee4d..0fa0182fbd 100644
--- a/xen/arch/x86/mm/hap/p2m-ept.c
+++ b/xen/arch/x86/mm/hap/p2m-ept.c
@@ -579,8 +579,9 @@ static mfn_t ept_get_entry(struct p2m_domain *p2m,
             goto out;
     }
 
-
-    if ( ept_entry->sa_p2mt != p2m_invalid )
+    /* Need to check for all-zeroes because typecode 0 is p2m_ram and an
+     * entirely empty entry shouldn't have RAM type. */
+    if ( ept_entry->epte != 0 && ept_entry->sa_p2mt != p2m_invalid )
     {
         *t = ept_entry->sa_p2mt;
         *a = ept_entry->access;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 001883d256..a57464549f 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1883,9 +1883,6 @@ static mfn_t p2m_gfn_to_mfn_current(struct p2m_domain *p2m,
             p2mt = p2m_flags_to_type(l1e_get_flags(l1e));
             ASSERT(l1e_get_pfn(l1e) != INVALID_MFN || !p2m_is_ram(p2mt));
 
-            if ( l1e.l1 == 0 )
-                p2mt = p2m_invalid;
-
             if ( p2m_flags_to_type(l1e_get_flags(l1e))
                  == p2m_populate_on_demand )
             {
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 91b7ce6994..97c830a550 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -381,12 +381,12 @@ static inline p2m_type_t p2m_flags_to_type(unsigned long flags)
 {
     /* Type is stored in the "available" bits */
 #ifdef __x86_64__
-    /*
-     * AMD IOMMU: When we share p2m table with iommu, bit 9 - bit 11 will be
-     * used for iommu hardware to encode next io page level. Bit 59 - bit 62
-     * are used for iommu flags, We could not use these bits to store p2m types.
-     */
-
+    /* For AMD IOMMUs we need to use type 0 for plain RAM, but we need
+     * to make sure that an entirely empty PTE doesn't have RAM type */
+    if ( flags == 0 ) 
+        return p2m_invalid;
+    /* AMD IOMMUs use bits 9-11 to encode next io page level and bits
+     * 59-62 for iommu flags so we can't use them to store p2m type info. */
     return (flags >> 12) & 0x7f;
 #else
     return (flags >> 9) & 0x7;