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

[Zhang, Xiong Y]

> On Fri, 31 Mar 2017 02:27:11 +0000
> "Zhang, Xiong Y" <address@hidden> wrote:
> 
> > > 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 ?
> 
> Yeah, that should do it.  x-vga should not be necessary, but shouldn't
> hurt IIRC.  Any dmesg errors regarding the ROM?  I think we have
> trouble with the ROM if the host is booted in UEFI mode.
[Zhang, Xiong Y] My host boot in legacy bios mode. After adding x-igd-gms in 
legacy mode, win 8.1 IGD driver could bind to IGD, and win 8.1 runs good. 
thanks
> 
> >
> > > Please clarify Gen9+, is this Kaby Lake?
> > [Zhang, Xiong Y] Gen 9+ is SkyLake and later.
> 
> Ok, then I cannot test since I only have access to BDW.  We do have
> users that might start complaining if this is a new change in the
> Windows driver for SKL+.
> 
> > > 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.
> 
> Ok, no problem.  Thanks,
> 
> Alex