Re: [Qemu-devel] hw/misc/pci-testdev.c write access does not work

[Paolo Bonzini]

On 08/07/2016 19:46, Alexander Gordeev wrote:
> Hi all,
> 
> Looks like hw/misc/pci-testdev.c does not work for wildcard-eventfd and
> datamatch-eventfd tests (more precisely - for any non no-eventfd tests).
> 
> Test writes to pci-testdev's addresses (reported by PCITestDevHdr::offset
> field) do not cause invocations of MemoryRegionOps::write() callback.
> 
> (I found that by putting debug output to pci_testdev_write() and using
> vmexit testcase from kvm-unit-tests).
> 
> The reason kvm-unit-tests does not hit this issue is because vmexit does
> not check number of successful writes reported via PCITestDevHdr::count
> field.

In the eventfd case, the writes are hijacked by KVM and cause an eventfd
write instead of invoking the callback.  The idea is that the written
value doesn't matter (or if it matters, it's matched via datamatch) and
eventually userspace will process the eventfd write in another thread.

So this is expected.

Paolo