Re: [Qemu-devel] ivshmem Windows Driver

[Ladi Prosek]

Hi Geoff,

On Mon, Oct 16, 2017 at 8:31 PM,  <address@hidden> wrote:
> Hi Yan & Ladi.
>
> I have written an initial implementation that supports just the shared
> memory
> mapping at this time. I plan to add events also but before I go further I
> would
> like some feedback if possible on what I have implemented thus far.
>
> Please see:
>
> https://github.com/gnif/kvm-guest-drivers-windows/commit/8655cf12fbdd77b991f96d97bc20f967b5907c12

Thank you, looks good overall.

* Please don't use the 'vio' prefix for this driver. ivshmem is not a
VirtIO device (i.e. not using the VirtIO protocol). Also the test
program should live in a subdirectory, so maybe something like
/ivshmem and /ivshmem/test.

* In VIOIVSHMEMEvtDevicePrepareHardware: I don't think that Windows
guarantees that resources are enumerated in BAR order. In VirtIO
drivers we read the PCI config space to identify the BAR index:
https://github.com/virtio-win/kvm-guest-drivers-windows/blob/master/VirtIO/VirtIOPCICommon.c#L353

* IOCTL codes on Windows have a structure to them:
https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/defining-i-o-control-codes

* In VIOIVSHMEMEvtIoDeviceControl: The "only one mapping at a time is
allowed" test has a race. I think that simply making the IO queue
WdfIoQueueDispatchSequential instead of WdfIoQueueDispatchParallel
will fix it.

* According to MSDN, MmMapLockedPagesSpecifyCache(UserMode) should be
wrapped in try/except. Also, what happens if the file handle is
inherited by a child process? Can it unmap the mapping in parent's
address space? What if the parent exits? A possible solution is
discussed in this article:
http://www.osronline.com/article.cfm?article=39

Thanks!
Ladi