On 2011-10-18 19:34, Avi Kivity wrote: > On 10/18/2011 06:49 PM, Jan Kiszka wrote: >> On 2011-10-18 18:40, Avi Kivity wrote: >>> On 10/18/2011 04:30 PM, Avi Kivity wrote: >>>> This takes a while to reproduce, let me talk to gdb for a bit. >>>> >>> >>> a vcpu exit causes kvm_flush_coalesced_mmio_buffer() to run, which does >>> a bitblt, which is cirrus_do_copy(), which goes to vga_hw_update, which >> >> Why does it have to do vga_hw_update? Why can't it set some flag for the >> next requested screen update or so? Just thinking, haven't looked at the >> code yet. > > Maybe it's a remnant from the days where it asked the host hardware to > do the blt.
If it's no longer needed - drop it? Already for other reasons like efficiency. > >> Do you think that only cirrus is affected by this pattern? > > It's also possible for hotunplug: > > - hotunplug > - unregister coalesced regions > - flush mmios > - call back into same device Which device triggers hotunplug via a coalesced mmio region? Anyway, if we want to avoid other surprises like that, better make kvm_flush_coalesced_mmio_buffer reentrance-safe. If we think that this remains an odd scenario, issue a warning to the console that some device may require fixing. Jan
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