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Re: [Qemu-devel] [PATCH] Revert "vfio/pci-quirks.c: Disable stolen memor

From: Alex Williamson
Subject: Re: [Qemu-devel] [PATCH] Revert "vfio/pci-quirks.c: Disable stolen memory for igd VFIO"
Date: Thu, 30 Mar 2017 20:55:11 -0600

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.

> > 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,


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