Re: [Xen-devel] [PATCH] VT-d: add iommu=igfx_off option to workaround graphics issues

[èæç <lantw44@xxxxxxxxx>]

Andrew Cooper æ èå2015å07æ18æ 03:36 åé:
> On 17/07/15 20:05, Ting-Wei Lan wrote:
> > When using Linux >= 3.19 (commit 47591df) as dom0 on some Intel Ironlake
> > devices, It is possible to encounter graphics issues that make screen
> > unreadable or crash the system. It was reported in freedesktop bugzilla:
> >
> > https://bugs.freedesktop.org/show_bug.cgi?id=90037
> >
> > As we still cannot find a proper fix for this problem, this patch adds
> > iommu=igfx_off option that is similar to Linux intel_iommu=igfx_off for
> > users to manually workaround the problem.
> >
> > Signed-off-by: Ting-Wei Lan <lantw44@xxxxxxxxx>
> If the identified Linux change is correct, then the problems is almost
> certainly the i915 driver not using appropriate cache flushing
> operations on memory of weakened caching type.
>
> Are there any details available on if/how/what snoop features the IGD
> and its IOMMU have?
How can I get these details? I get some messages from 'xl dmesg' or 
'lspci'. Are these messages related?
(XEN) PCI: Not using MCFG for segment 0000 bus 00-3f
(XEN) Intel VT-d iommu 1 supported page sizes: 4kB.
(XEN) Intel VT-d iommu 0 supported page sizes: 4kB.
(XEN) Intel VT-d iommu 2 supported page sizes: 4kB.
(XEN) Intel VT-d Snoop Control not enabled.
(XEN) Intel VT-d Dom0 DMA Passthrough not enabled.
(XEN) Intel VT-d Queued Invalidation not enabled.
(XEN) Intel VT-d Interrupt Remapping not enabled.
(XEN) Intel VT-d Shared EPT tables not enabled.
(XEN) I/O virtualisation enabled
(XEN)  - Dom0 mode: Relaxed
(XEN) Interrupt remapping disabled
(XEN) Enabled directed EOI with ioapic_ack_old on!
(XEN) ENABLING IO-APIC IRQs
(XEN)  -> Using old ACK method
(XEN) Platform timer is 14.318MHz HPET
(XEN) Allocated console ring of 16 KiB.
(XEN) VMX: Supported advanced features:
(XEN)  - APIC MMIO access virtualisation
(XEN)  - APIC TPR shadow
(XEN)  - Extended Page Tables (EPT)
(XEN)  - Virtual-Processor Identifiers (VPID)
(XEN)  - Virtual NMI
(XEN)  - MSR direct-access bitmap
(XEN)  - Unrestricted Guest
(XEN) HVM: ASIDs enabled.
(XEN) HVM: VMX enabled
(XEN) HVM: Hardware Assisted Paging (HAP) detected
(XEN) HVM: HAP page sizes: 4kB, 2MB

00:02.0 VGA compatible controller: Intel Corporation Core Processor 
Integrated Graphics Controller (rev 12) (prog-if 00 [VGA controller])
        Subsystem: ASUSTeK Computer Inc. Device 8383
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR- FastB2B- DisINTx+
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin A routed to IRQ 64
        Region 0: Memory at f7400000 (64-bit, non-prefetchable) [size=4M]
        Region 2: Memory at e0000000 (64-bit, prefetchable) [size=256M]
        Region 4: I/O ports at bc00 [size=8]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
                Address: fee0400c  Data: 4191
        Capabilities: [d0] Power Management version 2
                Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA 
PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [a4] PCI Advanced Features
                AFCap: TP+ FLR+
                AFCtrl: FLR-
                AFStatus: TP-
        Kernel driver in use: i915
        Kernel modules: i915

Can we get useful information from these Intel datasheets?
http://www.intel.com/content/www/us/en/processors/pentium/core-i5-600-i3-500-pentium-6000-datasheet-vol-1.html
http://www.intel.com/content/www/us/en/processors/pentium/core-i5-600-i3-500-pentium-6000-datasheet-vol-2.html

> ~Andrew

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