Re: [Qemu-devel] [PATCH] Revert "vfio/pci-quirks.c: Disable stolen memory for igd VFIO"

[Zhang, Xiong Y]

> On Thu, 30 Mar 2017 18:27:21 +0800
> Xiong Zhang <address@hidden> wrote:
> 
> > This reverts commit c2b2e158cc7b1cb431bd6039824ec13c3184a775.
> >
> > The original patch intend to prevent linux i915 driver from using
> > stolen meory. But this patch breaks windows IGD driver loading on
> > Gen9+, as IGD HW will use stolen memory on Gen9+, once windows IGD
> > driver see zero size stolen memory, it will unload.
> > Meanwhile stolen memory will be disabled in 915 when i915 run as
> > a guest.
> 
> Does this mean that legacy mode IGD assignment is not going to work
> on Gen9+ with Windows?  Will it continue to work with Gen8-?
[Zhang, Xiong Y] I try to use the following qemu command to enable legacy mode 
on SKyLake, but It seems the entry point of wins IGD driver isn't called(I 
couldn't confirm this as I don't have the source code, but I didn't see any IGD 
driver info from windbg while I could see many info in upt mode), so driver 
doesn't bind to IGD after win 8.1 boot up.
  #qemu-system-x86_64 -M pc -enable-kvm -smp 2 -m 2G  -vga none -nographic -cpu 
host -hda "$IMAGE" -device 
vfio-pci,host=00:02.0,x-vga=true,id=hostdev0,bus=pci.0,addr=0x2
Is this the right method to enable legacy mode ?

> Please clarify Gen9+, is this Kaby Lake?
[Zhang, Xiong Y] Gen 9+ is SkyLake and later.

> I assume this patch is intended for QEMU 2.9, it's helpful to make that
> explicit during the rc freeze.  Thanks,
[Zhang, Xiong Y] Yes, as the original patch has entered into Qemu 2.9 rc1. So 
this reverted patch should be entered into the later 2.9 rc.
Sorry for the troubles.