[Xen-devel] [PATCH] x86emul: refine VME/PVI early #GP check

["Jan Beulich" <JBeulich@xxxxxxxx>]

In commit efe9cba66c ("x86emul: VME and PVI modes require a #GP(0) check
first thing") I neglected the fact that the retire flags get zapped only
in x86_decode(), which hasn't been invoked yet at the point of the #GP(0)
check added.

Ahead of the other explicit return (rather than "goto") path use an
explicit return here too, to make the flow more obvious.

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

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -3400,10 +3400,15 @@ x86_emulate(
 
     ASSERT(ops->read);
 
-    generate_exception_if((mode_vif() &&
-                           (_regs.eflags & X86_EFLAGS_VIF) &&
-                           (_regs.eflags & X86_EFLAGS_VIP)),
-                          EXC_GP, 0);
+    if ( unlikely(mode_vif()) &&
+         (_regs.eflags & X86_EFLAGS_VIF) &&
+         (_regs.eflags & X86_EFLAGS_VIP) )
+    {
+        x86_emul_hw_exception(EXC_GP, 0, ctxt);
+        /* x86_decode() was not called yet. */
+        ctxt->retire.raw = 0;
+        return X86EMUL_EXCEPTION;
+    }
 
     rc = x86_decode(&state, ctxt, ops);
     if ( rc != X86EMUL_OKAY )





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