[Xen-changelog] [qemu-upstream-unstable] exec: change default exception_index value for migration to -1

[patchbot@xxxxxxx]

commit a97f9a7ec720d6f141cf4ee825f5c54c48747457
Author:     Paolo Bonzini <pbonzini@xxxxxxxxxx>
AuthorDate: Fri Dec 19 12:53:14 2014 +0100
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue Feb 24 15:17:35 2015 -0600

    exec: change default exception_index value for migration to -1
    
    In QEMU 2.2 the exception_index value was added to the migration stream
    through a subsection.  The default was set to 0, which is wrong and
    should have been -1.
    
    However, 2.2 does not have commit e511b4d (cpu-exec: reset exception_index
    correctly, 2014-11-26), hence in 2.2 the exception_index is never used
    and is set to -1 on the next call to cpu_exec.  So we can change the
    migration stream to make the default -1.  The effects are:
    
    - 2.2.1 -> 2.2.0: cpu->exception_index set incorrectly to 0 if it
    were -1 on the source; then reset to -1 in cpu_exec.  This is TCG
    only; KVM does not use exception_index.
    
    - 2.2.0 -> 2.2.1: cpu->exception_index set incorrectly to -1 if it
    were 0 on the source; but it would be reset to -1 in cpu_exec anyway.
    This is TCG only; KVM does not use exception_index.
    
    - 2.2.1 -> 2.1: two bugs fixed: 1) can migrate backwards if
    cpu->exception_index is set to -1; 2) should not migrate backwards
    (but 2.2.0 allows it) if cpu->exception_index is set to 0
    
    - 2.2.0 -> 2.3.0: 2.2.0 will send the subsection unnecessarily if
    exception_index is -1, but that is not a problem.  2.3.0 will set
    cpu->exception_index to -1 if it is 0 on the source, but this would
    be anyway a problem for 2.2.0 -> 2.2.x migration (due to lack of
    commit e511b4d in 2.2.x) so we can ignore it
    
    - 2.2.1 -> 2.3.0: everything works.
    
    In addition, play it safe and never send the subsection unless TCG
    is in use.  KVM does not use exception_index (PPC KVM stores values
    in it for use in the subsequent call to ppc_cpu_do_interrupt, but
    does not need it as soon as kvm_handle_debug returns).  Xen and
    qtest do not run any code for the CPU at all.
    
    Reported-by: Igor Mammedov <imammedo@xxxxxxxxxx>
    Tested-by: Laurent Desnogues <laurent.desnogues@xxxxxxxxx>
    Tested-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Message-id: 1418989994-17244-3-git-send-email-pbonzini@xxxxxxxxxx
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Signed-off-by: Peter Maydell <peter.maydell@xxxxxxxxxx>
    (cherry picked from commit adee64249ee37e822d578e65a765750e7f2081f6)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 exec.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/exec.c b/exec.c
index 71ac104..46fe70e 100644
--- a/exec.c
+++ b/exec.c
@@ -434,7 +434,7 @@ static int cpu_common_pre_load(void *opaque)
 {
     CPUState *cpu = opaque;
 
-    cpu->exception_index = 0;
+    cpu->exception_index = -1;
 
     return 0;
 }
@@ -443,7 +443,7 @@ static bool cpu_common_exception_index_needed(void *opaque)
 {
     CPUState *cpu = opaque;
 
-    return cpu->exception_index != 0;
+    return tcg_enabled() && cpu->exception_index != -1;
 }
 
 static const VMStateDescription vmstate_cpu_common_exception_index = {
--
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

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