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    SubjectRe: Broken pci_block_user_cfg_access interface
    On 2011-08-25 20:19, Michael S. Tsirkin wrote:
    > On Thu, Aug 25, 2011 at 03:06:01PM +0200, Jan Kiszka wrote:
    >>> I took a look at the sysfs triggered pci reset function and don't see any way
    >>> that the controlling device driver ever gets to be involved in this reset.
    >>> If code outside the ipr driver were to reset the adapter, the adapter firmware
    >>> would be left in an uninitialized state and until scsi core starts timing
    >>> out ops and driving EH, the card would be unusable. I can't imagine the
    >>> ipr driver is unique in this.
    >> Right, that's why a PCI core service is needed for coordination.
    >> Jan
    > But why do we want to trigger reset through sysfs while the
    > driver runs?

    A perfectly valid race conditions are created by KVM and VFIO: shared
    IRQ handler is triggered while the user space part wants to reset the
    assigned device. I'm quite sure that this how I first caused this bug to
    show up (it triggered for an assigned device with a shared busy IRQ line
    during QEMU startup, ie. the initial guest reset).


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