[Intel-gfx] [PATCH V5] drm/i915: Disable stolen memory when i915 runs on qemu

[Zhang, Xiong Y]

> On Wed, 12 Apr 2017 20:20:00 +0800
> Xiong Zhang <xiong.y.zhang at intel.com> wrote:
> 
> > Stolen memory isn't a standard pci resource and exists in RMRR which has
> > identity mapping in iommu table, IGD could access stolen memory in host
> OS.
> > While according to 'commit c875d2c1b808 ("iommu/vt-d: Exclude devices
> using
> > RMRRs from IOMMU API domains")',RMRR isn't supported by kvm, then
> both EPT
> > and guest iommu domain table lack of maaping for stolen memory in kvm
> IGD
> > passthrough environment. If IGD access stolen memory in such environment,
> > many iommu exceptions exist in host dmesg and gpu hang exists also.
> > DMAR: [DMA Read] Request device [00:02.0] fault addr da012000
> > [fault reason 05] PTE Write access is not set
> > DMAR: [DMA Read] Request device [00:02.0] fault addr da2df000
> > [fault reason 06] PTE Read access is not set
> >
> > So stolen memory should be disabled in KVM IGD passthrough environment,
> > this patch detects such environment through the existence of qemu
> emulated
> > isa bridge.
> >
> > When the real ISA bridge is also passed through to guest, guest will have
> > two isa bridges: emulated and real. Qemu guarantees the busnum:devnum.
> > funcnum of emulated isa bridge is always less than the real one. Then
> > emulated isa bridge is always detected first by pci_get_class(ISA). So
> > stolen memory will be disabled in this case also.
> 
> Where does QEMU make this guarantee or any sort of guarantee wrt the
> ISA bridge?  Thanks,
> 
> Alex
> 
[Zhang, Xiong Y] In my guest environment I always see emulated devices 
are at head of pci device list, the passed through devices are at tail. Even if
I want to assign the passed IGD to 00:02.0, the qemu tell me 00:02.0 has already
occupied by emulated graphic card.
If I pass through real ISA bridge to guest, the emulated ISA bridge is at 00:01.0,
While real ISA bridge is at 00:04.0.
Then I checked the code: emulated devices are created in pc_init1() function, it
creates host_bridge firstly, create isa_bridge secondly, create all other devices following.
So I think Qemu could guarantee. Now I'm suspect it, and need your coach. 

thanks