Re: [Qemu-devel] iommu emulation

[Alex Williamson]

On Wed, 15 Feb 2017 18:25:26 -0500
Jintack Lim <address@hidden> wrote:

> On Wed, Feb 15, 2017 at 5:50 PM, Alex Williamson <address@hidden
> > wrote:  
> 
> > On Wed, 15 Feb 2017 17:05:35 -0500
> > Jintack Lim <address@hidden> wrote:
> >  
> > > On Tue, Feb 14, 2017 at 9:52 PM, Peter Xu <address@hidden> wrote:
> > >  
> > > > On Tue, Feb 14, 2017 at 07:50:39AM -0500, Jintack Lim wrote:
> > > >
> > > > [...]
> > > >  
> > > > > > > >> > I misunderstood what you said?  
> > > > > > > >
> > > > > > > > I failed to understand why an vIOMMU could help boost  
> > performance.  
> > > > :(  
> > > > > > > > Could you provide your command line here so that I can try to
> > > > > > > > reproduce?  
> > > > > > >
> > > > > > > Sure. This is the command line to launch L1 VM
> > > > > > >
> > > > > > > qemu-system-x86_64 -M q35,accel=kvm,kernel-irqchip=split \
> > > > > > > -m 12G -device intel-iommu,intremap=on,eim=off,caching-mode=on \
> > > > > > > -drive file=/mydata/guest0.img,format=raw --nographic -cpu host  
> > \  
> > > > > > > -smp 4,sockets=4,cores=1,threads=1 \
> > > > > > > -device vfio-pci,host=08:00.0,id=net0
> > > > > > >
> > > > > > > And this is for L2 VM.
> > > > > > >
> > > > > > > ./qemu-system-x86_64 -M q35,accel=kvm \
> > > > > > > -m 8G \
> > > > > > > -drive file=/vm/l2guest.img,format=raw --nographic -cpu host \
> > > > > > > -device vfio-pci,host=00:03.0,id=net0  
> > > > > >
> > > > > > ... here looks like these are command lines for L1/L2 guest, rather
> > > > > > than L1 guest with/without vIOMMU?
> > > > > >  
> > > > >
> > > > > That's right. I thought you were asking about command lines for L1/L2 
> > > > >  
> > > > guest  
> > > > > :(.
> > > > > I think I made the confusion, and as I said above, I didn't mean to  
> > talk  
> > > > > about the performance of L1 guest with/without vIOMMO.
> > > > > We can move on!  
> > > >
> > > > I see. Sure! :-)
> > > >
> > > > [...]
> > > >  
> > > > > >
> > > > > > Then, I *think* above assertion you encountered would fail only if
> > > > > > prev == 0 here, but I still don't quite sure why was that  
> > happening.  
> > > > > > Btw, could you paste me your "lspci -vvv -s 00:03.0" result in  
> > your L1  
> > > > > > guest?
> > > > > >  
> > > > >
> > > > > Sure. This is from my L1 guest.  
> > > >
> > > > Hmm... I think I found the problem...
> > > >  
> > > > >
> > > > > address@hidden:~# lspci -vvv -s 00:03.0
> > > > > 00:03.0 Network controller: Mellanox Technologies MT27500 Family
> > > > > [ConnectX-3]
> > > > > Subsystem: Mellanox Technologies Device 0050
> > > > > 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, Cache Line Size: 64 bytes
> > > > > Interrupt: pin A routed to IRQ 23
> > > > > Region 0: Memory at fe900000 (64-bit, non-prefetchable) [size=1M]
> > > > > Region 2: Memory at fe000000 (64-bit, prefetchable) [size=8M]
> > > > > Expansion ROM at fea00000 [disabled] [size=1M]
> > > > > Capabilities: [40] Power Management version 3
> > > > > Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA  
> > PME(D0-,D1-,D2-,D3hot-,D3cold-  
> > > > )  
> > > > > Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
> > > > > Capabilities: [48] Vital Product Data
> > > > > Product Name: CX354A - ConnectX-3 QSFP
> > > > > Read-only fields:
> > > > > [PN] Part number: MCX354A-FCBT
> > > > > [EC] Engineering changes: A4
> > > > > [SN] Serial number: MT1346X00791
> > > > > [V0] Vendor specific: PCIe Gen3 x8
> > > > > [RV] Reserved: checksum good, 0 byte(s) reserved
> > > > > Read/write fields:
> > > > > [V1] Vendor specific: N/A
> > > > > [YA] Asset tag: N/A
> > > > > [RW] Read-write area: 105 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 253 byte(s) free
> > > > > [RW] Read-write area: 252 byte(s) free
> > > > > End
> > > > > Capabilities: [9c] MSI-X: Enable+ Count=128 Masked-
> > > > > Vector table: BAR=0 offset=0007c000
> > > > > PBA: BAR=0 offset=0007d000
> > > > > Capabilities: [60] Express (v2) Root Complex Integrated Endpoint,  
> > MSI 00  
> > > > > DevCap: MaxPayload 256 bytes, PhantFunc 0
> > > > > ExtTag- RBE+
> > > > > DevCtl: Report errors: Correctable- Non-Fatal+ Fatal+ Unsupported+
> > > > > RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop-
> > > > > MaxPayload 256 bytes, MaxReadReq 4096 bytes
> > > > > DevSta: CorrErr+ UncorrErr- FatalErr- UnsuppReq+ AuxPwr- TransPend-
> > > > > DevCap2: Completion Timeout: Range ABCD, TimeoutDis+, LTR-, OBFF Not
> > > > > Supported
> > > > > DevCtl2: Completion Timeout: 65ms to 210ms, TimeoutDis-, LTR-, OBFF  
> > > > Disabled  
> > > > > Capabilities: [100 v0] #00  
> > > >
> > > > Here we have the head of ecap capability as cap_id==0, then when we
> > > > boot the l2 guest with the same device, we'll first copy this
> > > > cap_id==0 cap, then when adding the 2nd ecap, we'll probably encounter
> > > > problem since pcie_find_capability_list() will thought there is no cap
> > > > at all (cap_id==0 is skipped).
> > > >
> > > > Do you want to try this "hacky patch" to see whether it works for you?
> > > >  
> > >
> > > Thanks for following this up!
> > >
> > > I just tried this, and I got some different message this time.
> > >
> > > qemu-system-x86_64: vfio: Cannot reset device 0000:00:03.0, no available
> > > reset mechanism.
> > > qemu-system-x86_64: vfio: Cannot reset device 0000:00:03.0, no available
> > > reset mechanism.  
> >
> > Possibly very true, it might affect the reliability of the device in
> > the l2 guest, but shouldn't prevent it from being assigned.  What's the
> > reset mechanism on the physical device (lspci -vvv from host please).
> >  
> 
> Thanks, Alex.
> This is from the host (L0).
> 
> 08:00.0 Network controller: Mellanox Technologies MT27500 Family
> [ConnectX-3]
> Subsystem: Mellanox Technologies Device 0050
> 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-
> Interrupt: pin A routed to IRQ 31
> Region 0: Memory at d9f00000 (64-bit, non-prefetchable) [disabled] [size=1M]
> Region 2: Memory at d5000000 (64-bit, prefetchable) [disabled] [size=8M]
> Expansion ROM at d9000000 [disabled] [size=1M]
> Capabilities: [40] Power Management version 3
> Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
> Status: D3 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-

Does not support reset on D3->D0 transition.

> Capabilities: [60] Express (v2) Endpoint, MSI 00
> DevCap: MaxPayload 512 bytes, PhantFunc 0, Latency L0s <64ns, L1 unlimited
> ExtTag- AttnBtn- AttnInd- PwrInd- RBE+ FLReset-

Does not support PCIe FLR.

No AF capability.  Looks right to me, the only mechanism available to
the host is a bus reset, which isn't available to the VM.  If you were
to configure it downstream of a root port, the VM might think it could
reset the device, but I'm pretty sure it cannot.  Thanks,

Alex