[Xen-devel] [PATCH v7 1/2] add a new p2m type class - P2M_DISCARD_WRITE_TYPES

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

From: Yu Zhang <yu.c.zhang@xxxxxxxxx>

Currently, the P2M_RO_TYPES bears 2 meanings: one is
"_PAGE_RW bit is clear in their PTEs", and another is
to discard the write operations on these pages. This
patch adds a p2m type class, P2M_DISCARD_WRITE_TYPES,
to bear the second meaning, so we can use this type
class instead of the P2M_RO_TYPES, to decide if a write
operation is to be ignored.

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Reviewed-by: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c         | 16 +++-------------
 xen/arch/x86/mm/shadow/multi.c |  2 +-
 xen/include/asm-x86/p2m.h      |  5 +++++
 3 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index bc414ff..2eb0795 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2837,7 +2837,7 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long 
gla,
      * to the mmio handler.
      */
     if ( (p2mt == p2m_mmio_dm) || 
-         (npfec.write_access && (p2mt == p2m_ram_ro)) )
+         (npfec.write_access && (p2m_is_discard_write(p2mt))) )
     {
         put_gfn(p2m->domain, gfn);
 
@@ -2882,16 +2882,6 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long 
gla,
         goto out_put_gfn;
     }
 
-    /* Shouldn't happen: Maybe the guest was writing to a r/o grant mapping? */
-    if ( npfec.write_access && (p2mt == p2m_grant_map_ro) )
-    {
-        gdprintk(XENLOG_WARNING,
-                 "trying to write to read-only grant mapping\n");
-        hvm_inject_hw_exception(TRAP_gp_fault, 0);
-        rc = 1;
-        goto out_put_gfn;
-    }
-
     /* If we fell through, the vcpu will retry now that access restrictions 
have
      * been removed. It may fault again if the p2m entry type still requires 
so.
      * Otherwise, this is an error condition. */
@@ -3941,7 +3931,7 @@ static enum hvm_copy_result __hvm_copy(
 
         if ( flags & HVMCOPY_to_guest )
         {
-            if ( p2mt == p2m_ram_ro )
+            if ( p2m_is_discard_write(p2mt) )
             {
                 static unsigned long lastpage;
                 if ( xchg(&lastpage, gfn) != gfn )
@@ -4035,7 +4025,7 @@ static enum hvm_copy_result __hvm_clear(paddr_t addr, int 
size)
 
         p = (char *)__map_domain_page(page) + (addr & ~PAGE_MASK);
 
-        if ( p2mt == p2m_ram_ro )
+        if ( p2m_is_discard_write(p2mt) )
         {
             static unsigned long lastpage;
             if ( xchg(&lastpage, gfn) != gfn )
diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index 225290e..94cf06d 100644
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -4575,7 +4575,7 @@ static mfn_t emulate_gva_to_mfn(struct vcpu *v,
     {
         return _mfn(BAD_GFN_TO_MFN);
     }
-    if ( p2m_is_readonly(p2mt) )
+    if ( p2m_is_discard_write(p2mt) )
     {
         put_page(page);
         return _mfn(READONLY_GFN);
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 5f7fe71..42de75d 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -113,6 +113,10 @@ typedef unsigned int p2m_query_t;
                       | p2m_to_mask(p2m_grant_map_ro)   \
                       | p2m_to_mask(p2m_ram_shared) )
 
+/* Write-discard types, which should discard the write operations */
+#define P2M_DISCARD_WRITE_TYPES (p2m_to_mask(p2m_ram_ro)     \
+                      | p2m_to_mask(p2m_grant_map_ro))
+
 /* Types that can be subject to bulk transitions. */
 #define P2M_CHANGEABLE_TYPES (p2m_to_mask(p2m_ram_rw) \
                               | p2m_to_mask(p2m_ram_logdirty) )
@@ -145,6 +149,7 @@ typedef unsigned int p2m_query_t;
 #define p2m_is_hole(_t) (p2m_to_mask(_t) & P2M_HOLE_TYPES)
 #define p2m_is_mmio(_t) (p2m_to_mask(_t) & P2M_MMIO_TYPES)
 #define p2m_is_readonly(_t) (p2m_to_mask(_t) & P2M_RO_TYPES)
+#define p2m_is_discard_write(_t) (p2m_to_mask(_t) & P2M_DISCARD_WRITE_TYPES)
 #define p2m_is_changeable(_t) (p2m_to_mask(_t) & P2M_CHANGEABLE_TYPES)
 #define p2m_is_pod(_t) (p2m_to_mask(_t) & P2M_POD_TYPES)
 #define p2m_is_grant(_t) (p2m_to_mask(_t) & P2M_GRANT_TYPES)
-- 
1.9.1


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