[Xen-bugs] [Bug 574] New: qemu pcnet emulation race causes data corruption

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=574

           Summary: qemu pcnet emulation race causes data corruption
           Product: Xen
           Version: unstable
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Tools
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: brazilnut@xxxxxxxxxx
                CC: niv@xxxxxxxxxx


The qemu pcnet hardware emulation violates the hardware interface by writing the
transmit and receive descriptors as a serial block of 16 bytes.  The second
word, tmd1 or rmd1, must be the first part of the descriptor read and the last
part written when updating the descriptor.  Otherwise the address read may be
stale, or the status seen by the driver may be stale.

This race is occasionally hit (30-50%) when transferring a large file from
another system, through dom0 to domU, when domU uses the pcnet32 driver. 
Possibly due to timing synchronization I can not get this to occur when going
from dom0 to domU alone.  The network asynchronous nature seems to be required
to hit this race.

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