[Xen-changelog] [xen-unstable] x86/hvm: don't leave emulator in inconsistent state

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1343317911 -3600
# Node ID ffcb24876b4f2e3c24be7db2a20318df81b0fc6c
# Parent  c29feacecfc4b0564b364adf0fd9c8bf19e250d8
x86/hvm: don't leave emulator in inconsistent state

The fact that handle_mmio(), and thus the instruction emulator, is
being run through twice for emulations that require involvement of the
device model, allows for the second run to see a different guest state
than the first one. Since only the MMIO-specific emulation routines
update the vCPU's io_state, if they get invoked on the second pass,
internal state (and particularly this variable) can be left in a state
making successful emulation of a subsequent MMIO operation impossible.

Consequently, whenever the emulator invocation returns without
requesting a retry of the guest instruction, reset io_state.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r c29feacecfc4 -r ffcb24876b4f xen/arch/x86/hvm/io.c
--- a/xen/arch/x86/hvm/io.c     Thu Jul 26 16:47:37 2012 +0100
+++ b/xen/arch/x86/hvm/io.c     Thu Jul 26 16:51:51 2012 +0100
@@ -179,6 +179,8 @@ int handle_mmio(void)
 
     rc = hvm_emulate_one(&ctxt);
 
+    if ( rc != X86EMUL_RETRY )
+        vio->io_state = HVMIO_none;
     if ( vio->io_state == HVMIO_awaiting_completion )
         vio->io_state = HVMIO_handle_mmio_awaiting_completion;
     else

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