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



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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