On Mon, 2015-03-16 at 12:04 +1100, Gavin Shan wrote: > > > (2) QEMU sends IOCTL commands to host to disable MSIx and enable INTx. At > this stage the INTx is still masked. At later point, the guest is requesting > unmasking INTx, which is captured by host. Host checks and founds pending > INTx, which is sent to QEMU. In QEMU INTx handler (vfio_intx_interrupt()), > the mmap'ed regions are disabled, "intx.pending" is set and a timer is started > to reenable mmap'ed regions if "intx.pending" is cleared there. However, > "intx.pending" is only cleared upon BAR access in slow path, which is never > happing. > > (3) After guest disables MSIx and issue EEH reset, the device driver starts > to check its firmware state by reading MMIO register, which isn't completed > by QEMU VFIO BAR slow path (Note: fast path supported by mmaped regions have > been disabled). Eventually, the guest hangs on reading MMIO register. With > this patch applied to QEMU, I didn't see the problem again.
Note that it might be a good idea to disable INTx (and synchronize with a cfg read of some sort) around resetting a device. Otherwise, you may hit a known issue if the device is behind a switch and has sent the INTx "assert" message, and not the "deassert" one before it gets reset. That can cause the INTx to effectively be "stuck" in the switch preventing a subsequent one from being delivered. Cheers, Ben.
