[dpdk-dev] DPDK doesn't work with iommu=pt

Hiroshi Shimamoto h-shimamoto at ct.jp.nec.com
Tue Sep 30 03:02:09 CEST 2014
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> Subject: Re: [dpdk-dev] DPDK doesn't work with iommu=pt
> 
> 
> 
> On Mon, Sep 29, 2014 at 2:53 AM, Hiroshi Shimamoto <h-shimamoto at ct.jp.nec.com> wrote:
> > Hi,
> >
> >> Subject: Re: [dpdk-dev] DPDK doesn't work with iommu=pt
> >>
> >> iommu=pt effectively disables iommu for the kernel and iommu is
> >> enabled only for KVM.
> >> http://lwn.net/Articles/329174/
> >
> > thanks for pointing that.
> >
> > Okay, I think DPDK cannot handle IOMMU because of no kernel code in
> > DPDK application.
> >
> > And now, I think "iommu=pt" doesn't work correctly DMA on host PMD
> > causes DMAR fault which means IOMMU catches a wrong operation.
> > Will dig around "iommu=pt".
> >
> I agree with your analysis, It seems that a fairly recent patch (3~4) months has introduced a bug that confuses unprotected
> DMA access with an iommu access, by the device and produces an equivalent of a page fault.
> 
> >>
> >> Basically unless you have KVM running you can remove both lines for
> >> the same effect.
> >> On the other hand if you do have KVM and you do want iommu=on You can
> >> remove the iommu=pt for the same performance because AFAIK unlike the
> >> kernel drivers DPDK doesn't dma_map and dma_unman each and every
> >> ingress/egress packet (Please correct me if I'm wrong), and will not
> >> suffer any performance penalties.
> >
> > I also tried "iommu=on", but it didn't fix the issue.
> > I saw the same error messages in kernel.
> >
> 
> Just to clarify, what I suggested you to try is leaving only this string in the command line "intel_iommu=on".  w/o iommu=pt.
> But this would work iff DPDK can handle iota's (I/O virtual addresses).

okay, I tried with "intel_iommu=on" only, but nothing was changed.

By the way, in several testing and my investigation, I think the issue comes from
no DMAR entry for hw pass through mode.
So using VFIO which turns IOMMU always on seems to solve my issue.

Unbind devices from igb_uio, and bind them vfio-pci, run testpmd looks working.

thanks,
Hiroshi

> 
> >   [   46.978097] dmar: DRHD: handling fault status reg 2
> >   [   46.978120] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr aa010000
> >   DMAR:[fault reason 02] Present bit in context entry is clear
> >
> > thanks,
> > Hiroshi
> >
> >>
> >> FYI. Kernel NIC drivers:
> >> When iommu=on{,strict} the kernel network drivers will suffer a heavy
> >> performance penalty due to regular IOVA modifications (both HW and SW
> >> at fault here). Ixgbe and Mellanox reuse dma_mapped pages on the
> >> receive side to avoid this penalty, but still suffer from iommu on TX.
> >>
> >> On Fri, Sep 26, 2014 at 5:47 PM, Choi, Sy Jong <sy.jong.choi at intel.com> wrote:
> >> > Hi Shimamoto-san,
> >> >
> >> > There are a lot of sighting relate to "DMAR:[fault reason 06] PTE Read access is not set"
> >> > https://www.mail-archive.com/kvm@vger.kernel.org/msg106573.html
> >> >
> >> > This might be related to IOMMU, and kernel code.
> >> >
> >> > Here is what we know :-
> >> > 1) Disabling VT-d in bios also removed the symptom
> >> > 2) Switch to another OS distribution also removed the symptom
> >> > 3) even different HW we will not see the symptom. In my case, switch from Engineering board to EPSD board.
> >> >
> >> > Regards,
> >> > Choi, Sy Jong
> >> > Platform Application Engineer
> >> >
> >> >
> >> > -----Original Message-----
> >> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Hiroshi Shimamoto
> >> > Sent: Friday, September 26, 2014 5:14 PM
> >> > To: dev at dpdk.org
> >> > Cc: Hayato Momma
> >> > Subject: [dpdk-dev] DPDK doesn't work with iommu=pt
> >> >
> >> > I encountered an issue that DPDK doesn't work with "iommu=pt intel_iommu=on"
> >> > on HP ProLiant DL380p Gen8 server. I'm using the following environment;
> >> >
> >> >   HW: ProLiant DL380p Gen8
> >> >   CPU: E5-2697 v2
> >> >   OS: RHEL7
> >> >   kernel: kernel-3.10.0-123 and the latest kernel 3.17-rc6+
> >> >   DPDK: v1.7.1-53-gce5abac
> >> >   NIC: 82599ES
> >> >
> >> > When boot with "iommu=pt intel_iommu=on", I got the below message and no packets are handled.
> >> >
> >> >   [  120.809611] dmar: DRHD: handling fault status reg 2
> >> >   [  120.809635] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr aa010000
> >> >   DMAR:[fault reason 02] Present bit in context entry is clear
> >> >
> >> > How to reproduce;
> >> > just run testpmd
> >> > # ./testpmd -c 0xf -n 4 -- -i
> >> >
> >> > Configuring Port 0 (socket 0)
> >> > PMD: ixgbe_dev_tx_queue_setup(): sw_ring=0x7ffff54eafc0 hw_ring=0x7ffff4200000 dma_addr=0xaa000000
> >> > PMD: ixgbe_dev_tx_queue_setup(): Using full-featured tx code path
> >> > PMD: ixgbe_dev_tx_queue_setup():  - txq_flags = 0 [IXGBE_SIMPLE_FLAGS=f01]
> >> > PMD: ixgbe_dev_tx_queue_setup():  - tx_rs_thresh = 32 [RTE_PMD_IXGBE_TX_MAX_BURST=32]
> >> > PMD: ixgbe_dev_rx_queue_setup(): sw_ring=0x7ffff54ea740 hw_ring=0x7ffff4210000 dma_addr=0xaa010000
> >> > PMD: check_rx_burst_bulk_alloc_preconditions(): Rx Burst Bulk Alloc Preconditions: rxq->rx_free_thresh=0,
> >> RTE_PMD_IXGBE_RX_MAX_BURST=32
> >> > PMD: ixgbe_dev_rx_queue_setup(): Rx Burst Bulk Alloc Preconditions are not satisfied, Scattered Rx is requested,
> or
> >> RTE_LIBRTE_IXGBE_RX_ALLOW_BULK_ALLOC is not enabled (port=0, queue=0).
> >> > PMD: check_rx_burst_bulk_alloc_preconditions(): Rx Burst Bulk Alloc Preconditions: rxq->rx_free_thresh=0,
> >> RTE_PMD_IXGBE_RX_MAX_BURST=32
> >> >
> >> > testpmd> start
> >> >   io packet forwarding - CRC stripping disabled - packets/burst=32
> >> >   nb forwarding cores=1 - nb forwarding ports=2
> >> >   RX queues=1 - RX desc=128 - RX free threshold=0
> >> >   RX threshold registers: pthresh=8 hthresh=8 wthresh=0
> >> >   TX queues=1 - TX desc=512 - TX free threshold=0
> >> >   TX threshold registers: pthresh=32 hthresh=0 wthresh=0
> >> >   TX RS bit threshold=0 - TXQ flags=0x0
> >> >
> >> >
> >> > and ping from another box to this server.
> >> > # ping6 -I eth2 ff02::1
> >> >
> >> > I got the below error message and no packet is received.
> >> > I couldn't see any increase RX/TX count in testpmt statistics
> >> >
> >> > testpmd> show port stats 0
> >> >
> >> >   ######################## NIC statistics for port 0  ########################
> >> >   RX-packets: 6          RX-missed: 0          RX-bytes:  732
> >> >   RX-badcrc:  0          RX-badlen: 0          RX-errors: 0
> >> >   RX-nombuf:  0
> >> >   TX-packets: 0          TX-errors: 0          TX-bytes:  0
> >> >   ############################################################################
> >> > testpmd> show port stats 0
> >> >
> >> >   ######################## NIC statistics for port 0  ########################
> >> >   RX-packets: 6          RX-missed: 0          RX-bytes:  732
> >> >   RX-badcrc:  0          RX-badlen: 0          RX-errors: 0
> >> >   RX-nombuf:  0
> >> >   TX-packets: 0          TX-errors: 0          TX-bytes:  0
> >> >   ############################################################################
> >> >
> >> >
> >> > The fault addr in error message must be RX DMA descriptor
> >> >
> >> > error message
> >> >   [  120.809635] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr aa010000
> >> >
> >> > log in testpmd
> >> >   PMD: ixgbe_dev_rx_queue_setup(): sw_ring=0x7ffff54ea740 hw_ring=0x7ffff4210000 dma_addr=0xaa010000
> >> >
> >> > I think the NIC received a packet in fifo and try to put into memory with DMA.
> >> > Before starting DMA, the NIC get the target address from RX descriptors in RDBA register.
> >> > But accessing RX descriptors failed in IOMMU unit and reported it to the kernel.
> >> >
> >> >   DMAR:[fault reason 02] Present bit in context entry is clear
> >> >
> >> > The error message looks there is no valid entry in IOMMU.
> >> >
> >> > I think the following issue is very similar, but using Ubuntu14.04 couldn't fix in my case.
> >> > http://thread.gmane.org/gmane.comp.networking.dpdk.devel/2281
> >> >
> >> > I tried Ubuntu14.04.1 and got the below error.
> >> >
> >> >   [  199.710191] dmar: DRHD: handling fault status reg 2
> >> >   [  199.710896] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr 7c24df000
> >> >   [  199.710896] DMAR:[fault reason 06] PTE Read access is not set
> >> >
> >> > Currently I could see this issue on HP ProLiant DL380p Gen8 only.
> >> > Is there any idea?
> >> > Has anyone noticed this issue?
> >> >
> >> > Note: we're thinking to use SR-IOV and DPDK app in the same box.
> >> > The box has 2 NICs, one for SR-IOV and pass through to VM, one (no SR-IOV) for DPDK app in host.
> >> >
> >> > thanks,
> >> > Hiroshi
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