[Xen-devel] [PATCH] ptwr_emulate adjustments

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

- really only do the invalid PAE PTE fixup on write to the high part
- dump guest execution state when emulation fails
- use the passed in register pointer rather than re-calculating
  guest_cpu_user_regs()

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Index: 2007-01-08/xen/arch/x86/mm.c
===================================================================
--- 2007-01-08.orig/xen/arch/x86/mm.c   2007-01-12 17:25:55.000000000 +0100
+++ 2007-01-08/xen/arch/x86/mm.c        2007-01-16 08:53:59.000000000 +0100
@@ -3237,22 +3237,25 @@ static int ptwr_emulated_update(
     {
         if ( (CONFIG_PAGING_LEVELS == 3 || IS_COMPAT(d)) &&
              (bytes == 4) &&
+             (addr & 4) &&
              !do_cmpxchg &&
              (l1e_get_flags(nl1e) & _PAGE_PRESENT) )
         {
             /*
-             * If this is a half-write to a PAE PTE then we assume that the
-             * guest has simply got the two writes the wrong way round. We
-             * zap the PRESENT bit on the assumption the bottom half will be
-             * written immediately after we return to the guest.
+             * If this is an upper half write to a PAE PTE then we assume
+             * that the guest has simply got the two writes the wrong way
+             * round. We zap the PRESENT bit on the assumption the bottom
+             * half will be written immediately after we return to the guest.
              */
             MEM_LOG("ptwr_emulate: fixing up invalid PAE PTE %"PRIpte,
                     l1e_get_intpte(nl1e));
+            show_execution_state(ptwr_ctxt->ctxt.regs);
             l1e_remove_flags(nl1e, _PAGE_PRESENT);
         }
         else
         {
             MEM_LOG("ptwr_emulate: could not get_page_from_l1e()");
+            show_execution_state(ptwr_ctxt->ctxt.regs);
             return X86EMUL_UNHANDLEABLE;
         }
     }
@@ -3375,7 +3378,8 @@ int ptwr_do_page_fault(struct vcpu *v, u
          (page_get_owner(page) != d) )
         goto bail;
 
-    ptwr_ctxt.ctxt.regs = guest_cpu_user_regs();
+    ASSERT(regs = guest_cpu_user_regs());
+    ptwr_ctxt.ctxt.regs = regs;
     ptwr_ctxt.ctxt.addr_size = ptwr_ctxt.ctxt.sp_size =
         IS_COMPAT(d) ? 32 : BITS_PER_LONG;
     ptwr_ctxt.cr2 = addr;


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