[PATCH v7 02/15] x86/mm: make sure there is one exit path for modify_xen_mappings

[Hongyan Xia <hx242@xen.org>]

From: Wei Liu <wei.liu2@citrix.com>

We will soon need to handle dynamically mapping / unmapping page
tables in the said function. Since dynamic mappings may map and unmap
pl3e in different iterations, lift pl3e out of the loop.

No functional change.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Hongyan Xia <hongyxia@amazon.com>

---
Changed since v4:
- drop the end_of_loop goto label.

Changed since v3:
- remove asserts on rc since it never gets changed to anything else.
---
 xen/arch/x86/mm.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index d99f9bc133..462682ba70 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5457,10 +5457,12 @@ int populate_pt_range(unsigned long virt, unsigned long nr_mfns)
 int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
 {
     bool locking = system_state > SYS_STATE_boot;
+    l3_pgentry_t *pl3e;
     l2_pgentry_t *pl2e;
     l1_pgentry_t *pl1e;
     unsigned int  i;
     unsigned long v = s;
+    int rc = -ENOMEM;
 
     /* Set of valid PTE bits which may be altered. */
 #define FLAGS_MASK (_PAGE_NX|_PAGE_RW|_PAGE_PRESENT)
@@ -5471,7 +5473,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
 
     while ( v < e )
     {
-        l3_pgentry_t *pl3e = virt_to_xen_l3e(v);
+        pl3e = virt_to_xen_l3e(v);
 
         if ( !pl3e || !(l3e_get_flags(*pl3e) & _PAGE_PRESENT) )
         {
@@ -5504,7 +5506,8 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
             /* PAGE1GB: shatter the superpage and fall through. */
             l2t = alloc_xen_pagetable();
             if ( !l2t )
-                return -ENOMEM;
+                goto out;
+
             for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++ )
                 l2e_write(l2t + i,
                           l2e_from_pfn(l3e_get_pfn(*pl3e) +
@@ -5561,7 +5564,8 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
                 /* PSE: shatter the superpage and try again. */
                 l1t = alloc_xen_pagetable();
                 if ( !l1t )
-                    return -ENOMEM;
+                    goto out;
+
                 for ( i = 0; i < L1_PAGETABLE_ENTRIES; i++ )
                     l1e_write(&l1t[i],
                               l1e_from_pfn(l2e_get_pfn(*pl2e) + i,
@@ -5694,7 +5698,10 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
     flush_area(NULL, FLUSH_TLB_GLOBAL);
 
 #undef FLAGS_MASK
-    return 0;
+    rc = 0;
+
+ out:
+    return rc;
 }
 
 #undef flush_area
-- 
2.24.1.AMZN