[Xen-devel] [PATCH v4 2/2] x86/mm: factor out the code for shattering an l2 PTE

[Hongyan Xia <hongyxia@xxxxxxxxxx>]

map_pages_to_xen and modify_xen_mappings are performing almost exactly
the same operations when shattering an l2 PTE, the only difference
being whether we want to flush.

Signed-off-by: Hongyan Xia <hongyxia@xxxxxxxxxx>

---
Changes in v4:
- use false/true instead of -1/0 to indicate failure/success.
- remove unnecessary cast.

Changes in v3:
- style and indentation changes.
- return -ENOMEM instead of -1.

Changes in v2:
- improve asm.
- re-read pl2e from memory when taking the lock.
- move the allocation of l1t inside the shatter function.
---
 xen/arch/x86/mm.c | 96 ++++++++++++++++++++++++-----------------------
 1 file changed, 49 insertions(+), 47 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 8def4fb8d8..4daf0ff0f0 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5151,6 +5151,52 @@ 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 l2 entry and populate l1. If virt is passed in, also do flush. */
+static bool shatter_l2e(l2_pgentry_t *pl2e, unsigned long virt, bool locking)
+{
+    unsigned int i;
+    l2_pgentry_t ol2e = *pl2e;
+    l1_pgentry_t l1e = l1e_from_paddr(l2e_get_paddr(ol2e),
+                                      lNf_to_l1f(l2e_get_flags(ol2e)));
+    l1_pgentry_t *l1t = alloc_xen_pagetable();
+
+    if ( !l1t )
+        return false;
+
+    for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
+    {
+        l1e_write(l1t + i, l1e);
+        l1e = l1e_from_intpte(l1e_get_intpte(l1e) + PAGE_SIZE);
+    }
+
+    if ( locking )
+        spin_lock(&map_pgdir_lock);
+    if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
+         (l2e_get_flags(*pl2e) & _PAGE_PSE) )
+    {
+        l2e_write_atomic(pl2e,
+            l2e_from_paddr(virt_to_maddr(l1t), __PAGE_HYPERVISOR));
+        l1t = NULL;
+    }
+    if ( locking )
+        spin_unlock(&map_pgdir_lock);
+
+    if ( virt )
+    {
+        unsigned int flush_flags =
+            FLUSH_TLB | FLUSH_ORDER(PAGETABLE_ORDER);
+
+        if ( l2e_get_flags(ol2e) & _PAGE_GLOBAL )
+            flush_flags |= FLUSH_TLB_GLOBAL;
+        flush_area(virt, flush_flags);
+    }
+
+    if ( l1t )
+        free_xen_pagetable(l1t);
+
+    return true;
+}
+
 /* Shatter an l3 entry and populate l2. If virt is passed in, also do flush. */
 static bool shatter_l3e(l3_pgentry_t *pl3e, unsigned long virt, bool locking)
 {
@@ -5364,9 +5410,6 @@ int map_pages_to_xen(
             }
             else if ( l2e_get_flags(*pl2e) & _PAGE_PSE )
             {
-                unsigned int flush_flags =
-                    FLUSH_TLB | FLUSH_ORDER(PAGETABLE_ORDER);
-
                 /* Skip this PTE if there is no change. */
                 if ( (((l2e_get_pfn(*pl2e) & ~(L1_PAGETABLE_ENTRIES - 1)) +
                        l1_table_offset(virt)) == mfn_x(mfn)) &&
@@ -5385,32 +5428,9 @@ int map_pages_to_xen(
                     goto check_l3;
                 }
 
-                pl1e = alloc_xen_pagetable();
-                if ( pl1e == NULL )
+                /* Pass virt to indicate we need to flush. */
+                if ( !shatter_l2e(pl2e, virt, locking) )
                     return -ENOMEM;
-
-                for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
-                    l1e_write(&pl1e[i],
-                              l1e_from_pfn(l2e_get_pfn(*pl2e) + i,
-                                           lNf_to_l1f(l2e_get_flags(*pl2e))));
-
-                if ( l2e_get_flags(*pl2e) & _PAGE_GLOBAL )
-                    flush_flags |= FLUSH_TLB_GLOBAL;
-
-                if ( locking )
-                    spin_lock(&map_pgdir_lock);
-                if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
-                     (l2e_get_flags(*pl2e) & _PAGE_PSE) )
-                {
-                    l2e_write_atomic(pl2e, l2e_from_mfn(virt_to_mfn(pl1e),
-                                                        __PAGE_HYPERVISOR));
-                    pl1e = NULL;
-                }
-                if ( locking )
-                    spin_unlock(&map_pgdir_lock);
-                flush_area(virt, flush_flags);
-                if ( pl1e )
-                    free_xen_pagetable(pl1e);
             }
 
             pl1e  = l2e_to_l1e(*pl2e) + l1_table_offset(virt);
@@ -5633,26 +5653,8 @@ int modify_xen_mappings(unsigned long s, unsigned long 
e, unsigned int nf)
             else
             {
                 /* PSE: shatter the superpage and try again. */
-                pl1e = alloc_xen_pagetable();
-                if ( !pl1e )
+                if ( !shatter_l2e(pl2e, 0, locking) )
                     return -ENOMEM;
-                for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
-                    l1e_write(&pl1e[i],
-                              l1e_from_pfn(l2e_get_pfn(*pl2e) + i,
-                                           l2e_get_flags(*pl2e) & ~_PAGE_PSE));
-                if ( locking )
-                    spin_lock(&map_pgdir_lock);
-                if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
-                     (l2e_get_flags(*pl2e) & _PAGE_PSE) )
-                {
-                    l2e_write_atomic(pl2e, l2e_from_mfn(virt_to_mfn(pl1e),
-                                                        __PAGE_HYPERVISOR));
-                    pl1e = NULL;
-                }
-                if ( locking )
-                    spin_unlock(&map_pgdir_lock);
-                if ( pl1e )
-                    free_xen_pagetable(pl1e);
             }
         }
         else
-- 
2.17.1


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