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    SubjectRe: Broken pci_block_user_cfg_access interface
    On Thu, Aug 25, 2011 at 08:52:08PM +0200, Jan Kiszka wrote:
    > 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.

    OK, that would be solved by blocking sysfs reset while
    config access is blocked, right?

    > 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).
    >
    > Jan
    >




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