Re: [Qemu-discuss] DMAR errors with iommu emulation enabled

[Alex Williamson]

On Tue, 7 Feb 2017 11:46:57 -0500
Jintack Lim <address@hidden> wrote:

> Adding CC and some more information.

$ ./scripts/get_maintainer.pl -f ./hw/i386/intel_iommu.c
get_maintainer.pl: No maintainers found, printing recent contributors.
get_maintainer.pl: Do not blindly cc: them on patches!  Use common sense.

"Michael S. Tsirkin" <address@hidden> (commit_signer:54/35=100%)
Peter Xu <address@hidden> (commit_signer:28/35=80%)
Paolo Bonzini <address@hidden> (commit_signer:6/35=17%)
Jason Wang <address@hidden> (commit_signer:5/35=14%)
"Radim Krčmář" <address@hidden> (commit_signer:5/35=14%)
address@hidden (open list:All patches CC here)
 
> On Tue, Feb 7, 2017 at 5:07 AM, Jintack Lim <address@hidden> wrote:
> > Hi,
> >
> > I'm getting DMAR errors during VM booting when I enable the iommu
> > emulation for the VM. I was not able to complete booting since the VM
> > gets really slow and just keep printing the error message (sym0:
> > unexpected disconnect) at a speed of one character per second.
> >
> > I have enabled the iommu emulation, but didn't assign any device to the VM.
> >
> > This is the kernel log from the VM  
> 
> I'm using 4.6.0-rc5+ kernel for the host and the VM.
> 
> Here's the full kernel log from the VM.
> https://paste.ubuntu.com/23948597/
> 
> >
> > [    6.087794] sym0: SCSI BUS has been reset.
> > [    6.087960] DMAR: DRHD: handling fault status reg 2
> > [    6.088001] DMAR: DMAR:[DMA Read] Request device [04:03.0] fault
> > addr fe281000
> > [    6.088001] DMAR:[fault reason 06] PTE Read access is not set
> > [    6.090513] scsi host1: sym-2.2.3
> > [    6.090567] sym0: unexpected disconnect
> > [    8.814929] sym0: unexpected disconnect
> > [   11.670251] sym0: unexpected disconnect
> >
> > I enabled iommu in the host (intel_iommu=on). I also enabled iommu in
> > the guest AND gave this option to the qemu (-device intel-iommu). I'm
> > using qemu 2.8.0 and libvirt 3.0.0.
> > I used <qemu:commandline> in libvirt xml to enable iommu emulation.
> > Here's the full libvirt xml.
> > http://paste.ubuntu.com/23946803/
> >
> > I did lspci -vvv and 04:03:0 is scsi device. Unfortunately, I lost
> > that information, and can't boot the VM now. I'll add this information
> > later if necessary.  
> 
> This is information about 04:03:0
> I got this from the another identical VM but not with the iommu emulation.
> 
> address@hidden:~# lspci -vvs 04:03.0
> 04:03.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a
> 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: 255, Cache Line Size: 64 bytes
> Interrupt: pin A routed to IRQ 23
> Region 0: I/O ports at c000 [size=256]
> Region 1: Memory at fe284000 (32-bit, non-prefetchable) [size=1K]
> Region 2: Memory at fe280000 (32-bit, non-prefetchable) [size=8K]
> Kernel driver in use: sym53c8xx
> 
> >
> > Any thoughts why this happens and how to fix?

Try a different disk controller in the VM?  Running virtual VT-d can't
automatically fix guest drivers that don't handle devices behind an
IOMMU correctly.  I don't know if that's the case, but I imagine 53c895a
has probably never been tested w/ VT-d emulation.  Note that when you
do get to the point off assigning a device to the VM, you're going to
need to build your own QEMU with patches from the mailing list, or
maybe wait a few days and they might make it to the git tree.  Thanks,

Alex