• Paolo Bonzini's avatar
    vl: allow "cont" from panicked state · df390768
    Paolo Bonzini authored
    After reporting the GUEST_PANICKED monitor event, QEMU stops the VM.
    The reason for this is that events are edge-triggered, and can be lost if
    management dies at the wrong time.  Stopping a panicked VM lets management
    know of a panic even if it has crashed; management can learn about the
    panic when it restarts and queries running QEMU processes.  The downside
    is of course that the VM will be paused while management is not running,
    but that is acceptable if it only happens with explicit "-device pvpanic".
    
    Upon learning of a panic, management (if configured to do so) can pick a
    variety of behaviors: leave the VM paused, reset it, destroy it.  In
    addition to all of these behaviors, it is possible to dump the VM core
    from the host.
    
    However, right now, the panicked state is irreversible, and can only be
    exited by resetting the machine.  This means that any policy decision
    is entirely in the hands of the host.  In particular there is no way to
    use the "reboot on panic" option together with pvpanic.
    
    This patch makes the panicked state reversible (and removes various
    workarounds that were there because of the state being irreversible).
    With this change, management has a wider set of possible policies: it
    can just log the crash and leave policy to the guest, it can leave the
    VM paused.  In particular, the "log the crash and continue" is implemented
    simply by sending a "cont" as soon as management learns about the panic.
    Management could also implement the "irreversible paused state" itself.
    And again, all such actions can be coupled with dumping the VM core.
    
    Unfortunately we cannot change the behavior of 1.6.0.  Thus, even if
    it uses "-device pvpanic", management should check for "cont" failures.
    If "cont" fails, management can then log that the VM remained paused
    and urge the administrator to update QEMU.
    Reviewed-by: default avatarLaszlo Ersek <lersek@redhat.com>
    Reviewed-by: default avatarLuiz Capitulino <lcapitulino@redhat.com>
    Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
    df390768
gdbstub.c 43.2 KB