Re: [Xen-devel] [patch] pae: tlbflush linear page table updates

[Gerd Knorr <kraxel@xxxxxxx>]

> No, it's actually the changeset
> 6056:a1f7e01b0990a378584e718e6d48eac38824fdb9 which broke it.

And it isn't the mod_l3 update which broke PAE, it's the
__not_mapped() removal.  Applying the bits below reversed
makes PAE boot again.

  Gerd

diff -r 663f0fb1e444 -r a1f7e01b0990 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Tue Aug  9 09:34:06 2005
+++ b/xen/arch/x86/mm.c Tue Aug  9 10:42:51 2005
@@ -2902,42 +2887,13 @@
     .cmpxchg8b_emulated = ptwr_emulated_cmpxchg8b
 };
 
-#if defined(__x86_64__)
-/*
- * Returns zero on if mapped, or -1 otherwise
- */
-static int __not_mapped(l2_pgentry_t *pl2e)
-{
-    unsigned long page = read_cr3();
-
-    page &= PAGE_MASK;
-    page = ((unsigned long *) __va(page))[l4_table_offset((unsigned 
long)pl2e)];
-    if ( !(page & _PAGE_PRESENT) ) 
-        return -1;        
-        
-    page &= PAGE_MASK;
-    page = ((unsigned long *) __va(page))[l3_table_offset((unsigned 
long)pl2e)];
-    if ( !(page & _PAGE_PRESENT) ) 
-        return -1;
-
-    page &= PAGE_MASK;
-    page = ((unsigned long *) __va(page))[l2_table_offset((unsigned 
long)pl2e)];
-    if ( !(page & _PAGE_PRESENT) )
-        return -1;
-
-    return 0;
-}
-#else
-#define __not_mapped(p) (0)
-#endif
-
 /* Write page fault handler: check if guest is trying to modify a PTE. */
 int ptwr_do_page_fault(struct domain *d, unsigned long addr)
 {
     unsigned long    pfn;
     struct pfn_info *page;
     l1_pgentry_t     pte;
-    l2_pgentry_t    *pl2e;
+    l2_pgentry_t    *pl2e, l2e;
     int              which;
     unsigned long    l2_idx;
 
@@ -2984,10 +2940,7 @@
     pl2e = &__linear_l2_table[l2_idx];
     which = PTWR_PT_INACTIVE;
 
-    if ( unlikely(__not_mapped(pl2e)) )
-        goto inactive;
-
-    if ( (l2e_get_pfn(*pl2e)) == pfn )
+    if ( (__get_user(l2e.l2, &pl2e->l2) == 0) && (l2e_get_pfn(l2e) == pfn) )
     {
         /*
          * Check the PRESENT bit to set ACTIVE mode.
@@ -2995,13 +2948,11 @@
          * ACTIVE p.t. (it may be the same p.t. mapped at another virt addr).
          * The ptwr_flush call below will restore the PRESENT bit.
          */
-        if ( likely(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
+        if ( likely(l2e_get_flags(l2e) & _PAGE_PRESENT) ||
              (d->arch.ptwr[PTWR_PT_ACTIVE].l1va &&
               (l2_idx == d->arch.ptwr[PTWR_PT_ACTIVE].l2_idx)) )
             which = PTWR_PT_ACTIVE;
     }
-
-  inactive:
 
     /*
      * If this is a multi-processor guest then ensure that the page is hooked

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