[Xen-devel] [PATCH v2 1/2] x86/mm: factor out the code for shattering an l3 PTE

[Hongyan Xia <hongyxia@amazon.com>]

map_pages_to_xen and modify_xen_mappings are performing almost exactly
the same operations when shattering an l3 PTE, the only difference
being whether we want to flush.

Signed-off-by: Hongyan Xia <hongyxia@amazon.com>

---
Changes in v2:
- improve asm.
- re-read pl3e from memory when taking the lock.
- move the allocation of l2t inside the shatter function.
---
 xen/arch/x86/mm.c | 97 +++++++++++++++++++++++------------------------
 1 file changed, 48 insertions(+), 49 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 7d4dd80a85..6188a968ff 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5151,6 +5151,51 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
                          flush_area_local((const void *)v, f) : \
                          flush_area_all((const void *)v, f))
 
+/* Shatter an l3 entry and populate l2. If virt is passed in, also do flush. */
+static int shatter_l3e(l3_pgentry_t *pl3e, unsigned long virt, bool locking)
+{
+    unsigned int i;
+    l3_pgentry_t ol3e;
+    l2_pgentry_t ol2e, *l2t = alloc_xen_pagetable();
+
+    if ( l2t == NULL )
+        return -1;
+
+    ol3e = *pl3e;
+    ol2e = l2e_from_intpte(l3e_get_intpte(ol3e));
+
+    for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
+    {
+        l2e_write(l2t + i, ol2e);
+        ol2e = l2e_from_intpte(
+                l2e_get_intpte(ol2e) + (1 << (PAGETABLE_ORDER + PAGE_SHIFT)));
+    }
+    if ( locking )
+        spin_lock(&map_pgdir_lock);
+    if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
+         (l3e_get_flags(*pl3e) & _PAGE_PSE) )
+    {
+        l3e_write_atomic(pl3e,
+                l3e_from_paddr((paddr_t)virt_to_maddr(l2t), __PAGE_HYPERVISOR));
+        l2t = NULL;
+    }
+    if ( locking )
+        spin_unlock(&map_pgdir_lock);
+    if ( virt )
+    {
+        unsigned int flush_flags =
+            FLUSH_TLB | FLUSH_ORDER(2 * PAGETABLE_ORDER);
+
+        if ( (l3e_get_flags(ol3e) & _PAGE_GLOBAL) )
+                flush_flags |= FLUSH_TLB_GLOBAL;
+        flush_area(virt, flush_flags);
+    }
+    if ( l2t )
+        free_xen_pagetable(l2t);
+
+    return 0;
+}
+
 int map_pages_to_xen(
     unsigned long virt,
     mfn_t mfn,
@@ -5244,9 +5289,6 @@ int map_pages_to_xen(
         if ( (l3e_get_flags(ol3e) & _PAGE_PRESENT) &&
              (l3e_get_flags(ol3e) & _PAGE_PSE) )
         {
-            unsigned int flush_flags =
-                FLUSH_TLB | FLUSH_ORDER(2 * PAGETABLE_ORDER);
-
             /* Skip this PTE if there is no change. */
             if ( ((l3e_get_pfn(ol3e) & ~(L2_PAGETABLE_ENTRIES *
                                          L1_PAGETABLE_ENTRIES - 1)) +
@@ -5267,33 +5309,9 @@ int map_pages_to_xen(
                 continue;
             }
 
-            pl2e = alloc_xen_pagetable();
-            if ( pl2e == NULL )
+            /* Pass virt to indicate we need to flush. */
+            if ( shatter_l3e(pl3e, virt, locking) )
                 return -ENOMEM;
-
-            for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
-                l2e_write(pl2e + i,
-                          l2e_from_pfn(l3e_get_pfn(ol3e) +
-                                       (i << PAGETABLE_ORDER),
-                                       l3e_get_flags(ol3e)));
-
-            if ( l3e_get_flags(ol3e) & _PAGE_GLOBAL )
-                flush_flags |= FLUSH_TLB_GLOBAL;
-
-            if ( locking )
-                spin_lock(&map_pgdir_lock);
-            if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
-                 (l3e_get_flags(*pl3e) & _PAGE_PSE) )
-            {
-                l3e_write_atomic(pl3e, l3e_from_mfn(virt_to_mfn(pl2e),
-                                                    __PAGE_HYPERVISOR));
-                pl2e = NULL;
-            }
-            if ( locking )
-                spin_unlock(&map_pgdir_lock);
-            flush_area(virt, flush_flags);
-            if ( pl2e )
-                free_xen_pagetable(pl2e);
         }
 
         pl2e = virt_to_xen_l2e(virt);
@@ -5578,27 +5596,8 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
             }
 
             /* PAGE1GB: shatter the superpage and fall through. */
-            pl2e = alloc_xen_pagetable();
-            if ( !pl2e )
+            if ( shatter_l3e(pl3e, 0, locking) )
                 return -ENOMEM;
-            for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
-                l2e_write(pl2e + i,
-                          l2e_from_pfn(l3e_get_pfn(*pl3e) +
-                                       (i << PAGETABLE_ORDER),
-                                       l3e_get_flags(*pl3e)));
-            if ( locking )
-                spin_lock(&map_pgdir_lock);
-            if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
-                 (l3e_get_flags(*pl3e) & _PAGE_PSE) )
-            {
-                l3e_write_atomic(pl3e, l3e_from_mfn(virt_to_mfn(pl2e),
-                                                    __PAGE_HYPERVISOR));
-                pl2e = NULL;
-            }
-            if ( locking )
-                spin_unlock(&map_pgdir_lock);
-            if ( pl2e )
-                free_xen_pagetable(pl2e);
         }
 
         /*
-- 
2.17.1


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