Re: [RFC PATCH 0/9] CXL 2.0 Support

[Ben Widawsky]

Hi Chris.

On 20-12-04 12:40:03, Chris Browy wrote:
> Hi Ben,
> 
> Trying to bring up the environment using the latest developments as follows:
> 
> 1. Linux kernel baseline version is cloned using
>      git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
>    Using master branch.  Merged the 9 CXL linux kernel patches manually and built kernel
> 
> 2. QEMU baseline version is cloned using
>      git clone https://gitlab.com/bwidawsk/qemu.git
> 
> 3. UEFI baseline is cloned using
>      git clone https://github.com/tianocore/edk2.git
>    Using master and built
> 
> 4. Now can run qemu as follows:
>      The qcow2 we use is based on Ubuntu 20.10 with updated with kernel from 1) above
> 
>      QEMU command:
> 
>      sudo qemu-system-x86_64 -nic \
>      user,hostfwd=tcp::2222-:22,hostfwd=tcp::1234-:1234 -machine \
>      type=pc-q35-4.0,hmat=on,accel=kvm -enable-kvm -cpu host -smp \
>      6,cores=6,threads=1,sockets=1 -m 8G -boot order=d -k 'en-us' -vga virtio \
>      -drive file=/home/chris/Downloads/AQCXL/ubuntu_20.qcow,format=qcow2 -drive \
>      if=pflash,format=raw,readonly,file=/home/chris/OVMF_CODE.fd \
>      -drive if=pflash,format=raw,file=/home/chris/OVMF_VARS.fd \
>      -object memory-backend-file,id=cxl-mem1,share,mem-path=/tmp/cxl-test/cxl,size=512M \
>      -device pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52,uid=0,len-window-base=1,\
>      window-base[0]=0x4c0000000,memdev[0]=cxl-mem1 \
>      -device cxl-rp,id=rp0,bus=cxl.0,addr=0.0,chassis=0,slot=0  \
>      -device cxl-type3,bus=rp0,memdev=cxl-mem1,id=cxl-pmem0,size=256M  2>&1 | tee -a \
>      /home/chris/Downloads/AQCXL/log/qemu.log
> 
>    The qemu options are derived from looking at the tests/qtests/cxl-test.c
>    along with the -hmat=on which seemed to make sense.
> 
>    The system boots and lspci -vvv shows the CXL device is enumerated.  But
>    no DOE capability register for CDAT access though (see below).  Otherwise the
>    DVSEC registers are present.

DOE is not supported yet in either Linux or QEMU. For us, CDAT isn't a high
priority yet so it likely won't be done for a while. I'd really like to see DOE
support added by someone - not me - so that we can wire it up. Not sure what
that would look like in the QEMU side.

> 
>    acpidump indicates the CXL0 and CXLM devices but no SRAT or HMAT tables are
>    in the dump which is curious.

I don't typically use HMAT, but I do have an SRAT in mine, so that's strange.
You should also have a CEDT.

> 
> 
> 35:00.0 Memory controller [0502]: Intel Corporation Device 0d93 (rev 01) (prog-if 10)
>     Subsystem: Red Hat, Inc. Device 1100
>     Physical Slot: 0
>     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
>     Region 0: Memory at c0a00000 (64-bit, non-prefetchable) [size=64K]
>     Region 2: Memory at c0a10000 (64-bit, non-prefetchable) [size=4K]
>     Capabilities: [80] Express (v2) Endpoint, MSI 00
>         DevCap: MaxPayload 128 bytes, PhantFunc 0, Latency L0s <64ns, L1 <1us
>             ExtTag- AttnBtn- AttnInd- PwrInd- RBE+ FLReset- SlotPowerLimit 0.000W
>         DevCtl: CorrErr- NonFatalErr- FatalErr- UnsupReq-
>             RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop-
>             MaxPayload 128 bytes, MaxReadReq 128 bytes
>         DevSta: CorrErr- NonFatalErr- FatalErr- UnsupReq- AuxPwr- TransPend-
>         LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s, Exit Latency L0s <64ns
>             ClockPM- Surprise- LLActRep- BwNot- ASPMOptComp-
>         LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- CommClk-
>             ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
>         LnkSta: Speed 2.5GT/s (ok), Width x1 (ok)
>             TrErr- Train- SlotClk- DLActive+ BWMgmt- ABWMgmt-
>         DevCap2: Completion Timeout: Not Supported, TimeoutDis-, NROPrPrP-, LTR-
>              10BitTagComp-, 10BitTagReq-, OBFF Not Supported, ExtFmt+, EETLPPrefix+, MaxEETLPPrefixes 4
>                EmergencyPowerReduction Not Supported, EmergencyPowerReductionInit-
>              FRS-, TPHComp-, ExtTPHComp-
>              AtomicOpsCap: 32bit- 64bit- 128bitCAS-
>         DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF Disabled
>              AtomicOpsCtl: ReqEn-
>         LnkCtl2: Target Link Speed: 2.5GT/s, EnterCompliance- SpeedDis-
>              Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-
>              Compliance De-emphasis: -6dB
>         LnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete-, EqualizationPhase1-
>              EqualizationPhase2-, EqualizationPhase3-, LinkEqualizationRequest-
>     Capabilities: [100 v1] Designated Vendor-Specific <?>
>     Capabilities: [138 v1] Designated Vendor-Specific <?>
>     Kernel driver in use: cxl_mem
> 
> Questions/Comments:
> -------------------
> 1. Linux
>   a. Is there a gitlab for the linux kernel patches for CXL?  This would
>      facilitate review and code modifications.

We're hopefully going to send out v2 in the next couple of days. I'll push the
repo somewhere as well.

> 
> 2. UEFI (edk2 from tianocore)
>   a. seems to only support CXL 1.1 which means only method #1 (Device
>      option ROM) of Coherent Device Attribute Table_1.02 spec
>      for CDAT handling is possible now.
> 
>      Does device option ROM need to be added to QEMU CXL setup?
> 
>      Can we add a CXL 1.1 emulated device?

Patches welcome :-). I know of other people who want this, but I only care about
2.0+, so I have no intention to implement it.

> 
>   b. lspci doesn’t show the existence of the DOE extended capability register
>      in the CXL CT3D (needed to support method #2).  Are there more patches?

As above, it's not supported. I'm hoping someone else will do that work since I
don't care about it just yet.

> 
> 3. Do you have example user programs to share or better yet the CXL 2.0
>    Sec 14.3.6.1 Application Layer/ Transaction layer test for CXL.mem?
> 

I don't have, mostly because I haven't actually implemented a lot of the real
CXL support. My primary concern was having the Linux driver be able to enumerate
devices and communicate with the device via the mailbox interface. v2 will
contain support for userspace to do this, which I think is a step toward what
you're asking for.

> 4. What are the userspace system APIs for targeting CXL HDM address domain?
>    Usually you can mmap a SPA if you know how to look it up.

I think Dan answered this in the other thread...

> 
> 
> Best Regards,
> Chris Browy
> 
> 
>