Re: [PATCH 0/8] hw/cxl: CXL emulation cleanups and minor fixes for upstream

[Gregory Price]

1) No stack traces present
2) Device usage appears to work, but cxl-cli fails to create a region, i
haven't checked why yet (also tried ndctl-75, same results)
3) There seems to be some other regression with the cxl_pmem_init
routine, because I get a stack trace in this setup regardless of whether
I apply the type-3 device commit.


All tests below with the previously posted DOE linux branch.
Base QEMU branch was Jonathan's 2023-1-11


DOE Branch - 2023-1-11 (HEAD) (all commits)

QEMU Config:
sudo /opt/qemu-cxl/bin/qemu-system-x86_64 \
-drive 
file=/var/lib/libvirt/images/cxl.qcow2,format=qcow2,index=0,media=disk,id=hd \
-m 3G,slots=4,maxmem=8G \
-smp 4 \
-machine type=q35,accel=kvm,cxl=on \
-enable-kvm \
-nographic \
-object memory-backend-ram,id=mem0,size=1G,share=on \
-device pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52 \
-device cxl-rp,id=rp0,bus=cxl.0,chassis=0,slot=0 \
-device cxl-type3,bus=rp0,volatile-memdev=mem0,id=cxl-mem0 \
-M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=1G

Result:  This worked, but cxl-cli could not create a region (will look
into this further later).




When running with a persistent memory configuration, I'm seeing a
kernel stack trace on cxl_pmem_init

Config:
sudo /opt/qemu-cxl/bin/qemu-system-x86_64 \
-drive 
file=/var/lib/libvirt/images/cxl.qcow2,format=qcow2,index=0,media=disk,id=hd \
-m 3G,slots=4,maxmem=4G \
-smp 4 \
-machine type=q35,accel=kvm,cxl=on \
-enable-kvm \
-nographic \
-device pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52 \
-device cxl-rp,port=0,id=rp0,bus=cxl.0,chassis=0,slot=0 \
-object memory-backend-file,id=cxl-mem0,mem-path=/tmp/mem0,size=1G \
-object memory-backend-file,id=cxl-lsa0,mem-path=/tmp/lsa0,size=1G \
-device cxl-type3,bus=rp0,persistent-memdev=cxl-mem0,lsa=cxl-lsa0,id=cxl-pmem0 \
-M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=1G


[   62.167518] BUG: kernel NULL pointer dereference, address: 00000000000004c0
[   62.185069] #PF: supervisor read access in kernel mode
[   62.198502] #PF: error_code(0x0000) - not-present page
[   62.211019] PGD 0 P4D 0
[   62.220521] Oops: 0000 [#1] PREEMPT SMP PTI
[   62.233457] CPU: 3 PID: 558 Comm: systemd-udevd Not tainted 6.2.0-rc1+ #1
[   62.252886] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 
rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.org 04/01/2014
[   62.258432] Adding 2939900k swap on /dev/zram0.  Priority:100 extents:1 
across:2939900k SSDscFS
[   62.285513] RIP: 0010:cxl_nvdimm_probe+0x8d/0x130 [cxl_pmem]
[   62.285529] Code: 85 c0 0f 85 90 00 00 00 f0 80 0c 24 40 f0 80 4c 24 08 10 
f0 80 4c 24 08 20 f0 80 4c 24 08 40 49 8d 84 24 b8 04 00 00 4c 89 0
[   62.285531] RSP: 0018:ffffacff0141fc38 EFLAGS: 00010202
[   62.285534] RAX: ffff97a8a37b84b8 RBX: ffff97a8a37b8000 RCX: 0000000000000000
[   62.285536] RDX: 0000000000000001 RSI: ffff97a8a37b8000 RDI: 00000000ffffffff
[   62.285537] RBP: ffff97a8a37b8000 R08: 0000000000000001 R09: 0000000000000001
[   62.285538] R10: 0000000000000001 R11: 0000000000000000 R12: ffff97a8a37b8000
[   62.285539] R13: ffff97a982c3dc28 R14: 0000000000000000 R15: 0000000000000000
[   62.285541] FS:  00007f2619829580(0000) GS:ffff97a9bca00000(0000) 
knlGS:0000000000000000
[   62.285542] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   62.285544] CR2: 00000000000004c0 CR3: 00000001056a8000 CR4: 00000000000006e0
[   62.285653] Call Trace:
[   62.285656]  <TASK>
[   62.285660]  cxl_bus_probe+0x17/0x50
[   62.285691]  really_probe+0xde/0x380
[   62.285695]  ? pm_runtime_barrier+0x50/0x90
[   62.285700]  __driver_probe_device+0x78/0x170
[   62.285846]  driver_probe_device+0x1f/0x90
[   62.285850]  __driver_attach+0xd2/0x1c0
[   62.285853]  ? __pfx___driver_attach+0x10/0x10
[   62.285856]  bus_for_each_dev+0x76/0xa0
[   62.285860]  bus_add_driver+0x1b1/0x200
[   62.285863]  driver_register+0x89/0xe0
[   62.285868]  ? __pfx_init_module+0x10/0x10 [cxl_pmem]
[   62.285874]  cxl_pmem_init+0x50/0xff0 [cxl_pmem]
[   62.285880]  do_one_initcall+0x6e/0x330
[   62.285888]  do_init_module+0x4a/0x200
[   62.285892]  __do_sys_finit_module+0x93/0xf0
[   62.285899]  do_syscall_64+0x5b/0x80
[   62.285904]  ? do_syscall_64+0x67/0x80
[   62.285906]  ? asm_exc_page_fault+0x22/0x30
[   62.285910]  ? lockdep_hardirqs_on+0x7d/0x100
[   62.285914]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
[   62.285917] RIP: 0033:0x7f2619b0afbd
[   62.285920] Code: 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 
f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 8
[   62.285922] RSP: 002b:00007ffcc516bf58 EFLAGS: 00000246 ORIG_RAX: 
0000000000000139
[   62.285924] RAX: ffffffffffffffda RBX: 00005557c0dcaa60 RCX: 00007f2619b0afbd
[   62.285925] RDX: 0000000000000000 RSI: 00007f261a18743c RDI: 0000000000000006
[   62.285926] RBP: 00007f261a18743c R08: 0000000000000000 R09: 00007f261a17bb52
[   62.285927] R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000020000
[   62.285928] R13: 00005557c0dbbce0 R14: 0000000000000000 R15: 00005557c0dc18a0
[   62.285932]  </TASK>
[   62.285933] Modules linked in: cxl_pmem(+) snd_pcm libnvdimm snd_timer snd 
joydev bochs cxl_mem drm_vram_helper parport_pc soundcore drm_ttm_g
[   62.285954] CR2: 00000000000004c0
[   62.288385] ---[ end trace 0000000000000000 ]---
[   63.203514] RIP: 0010:cxl_nvdimm_probe+0x8d/0x130 [cxl_pmem]
[   63.203562] Code: 85 c0 0f 85 90 00 00 00 f0 80 0c 24 40 f0 80 4c 24 08 10 
f0 80 4c 24 08 20 f0 80 4c 24 08 40 49 8d 84 24 b8 04 00 00 4c 89 0
[   63.203565] RSP: 0018:ffffacff0141fc38 EFLAGS: 00010202
[   63.203570] RAX: ffff97a8a37b84b8 RBX: ffff97a8a37b8000 RCX: 0000000000000000
[   63.203572] RDX: 0000000000000001 RSI: ffff97a8a37b8000 RDI: 00000000ffffffff
[   63.203574] RBP: ffff97a8a37b8000 R08: 0000000000000001 R09: 0000000000000001
[   63.203576] R10: 0000000000000001 R11: 0000000000000000 R12: ffff97a8a37b8000
[   63.203577] R13: ffff97a982c3dc28 R14: 0000000000000000 R15: 0000000000000000
[   63.203580] FS:  00007f2619829580(0000) GS:ffff97a9bca00000(0000) 
knlGS:0000000000000000
[   63.203583] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   63.203585] CR2: 00000000000004c0 CR3: 00000001056a8000 CR4: 00000000000006e0



Next i reverted the QEMU branch to the commit just before the type-3
volatile commit and used the old method of launching with a type-3 pmem
device

Config:
sudo /opt/qemu-cxl/bin/qemu-system-x86_64 \
-drive 
file=/var/lib/libvirt/images/cxl.qcow2,format=qcow2,index=0,media=disk,id=hd \
-m 2G,slots=4,maxmem=4G \
-smp 4 \
-machine type=q35,accel=kvm,cxl=on \
-enable-kvm \
-nographic \
-device pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52 \
-device cxl-rp,id=rp0,bus=cxl.0,chassis=0,slot=0 \
-object 
memory-backend-file,pmem=true,id=cxl-mem0,mem-path=/tmp/cxl-mem0,size=1G \
-object memory-backend-file,pmem=true,id=lsa0,mem-path=/tmp/cxl-lsa0,size=1G \
-device cxl-type3,bus=rp0,memdev=cxl-mem0,lsa=lsa0,id=cxl-pmem0 \
-M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=1G


Result: Similar stack trace
[   29.850023] BUG: kernel NULL pointer dereference, address: 00000000000004c0
[   29.882400] RIP: 0010:cxl_nvdimm_probe+0x8d/0x130 [cxl_pmem]
[   29.957485] Call Trace:
[   29.959067]  <TASK>
[   29.962176]  cxl_bus_probe+0x17/0x50
[   29.964940]  really_probe+0xde/0x380
[   29.969065]  ? pm_runtime_barrier+0x50/0x90
[   29.973419]  __driver_probe_device+0x78/0x170
[   29.977183]  driver_probe_device+0x1f/0x90
[   29.984212]  __driver_attach+0xd2/0x1c0
[   29.988463]  ? __pfx___driver_attach+0x10/0x10
[   29.992379]  bus_for_each_dev+0x76/0xa0
[   29.997040]  bus_add_driver+0x1b1/0x200
[   30.000368]  driver_register+0x89/0xe0
[   30.004579]  ? __pfx_init_module+0x10/0x10 [cxl_pmem]
[   30.012403]  cxl_pmem_init+0x50/0xff0 [cxl_pmem]
[   30.019394]  do_one_initcall+0x6e/0x330
[   30.024028]  do_init_module+0x4a/0x200
[   30.029243]  __do_sys_finit_module+0x93/0xf0
[   30.034943]  do_syscall_64+0x5b/0x80
[   30.039844]  ? do_syscall_64+0x67/0x80
[   30.045163]  ? do_syscall_64+0x67/0x80
[   30.049729]  ? lock_release+0x14b/0x440
[   30.054055]  ? seqcount_lockdep_reader_access.constprop.0+0x82/0x90
[   30.061039]  ? lock_is_held_type+0xe8/0x140
[   30.067625]  ? do_syscall_64+0x67/0x80
[   30.071909]  ? lockdep_hardirqs_on+0x7d/0x100
[   30.079037]  ? do_syscall_64+0x67/0x80
[   30.084537]  ? do_syscall_64+0x67/0x80
[   30.089091]  ? do_syscall_64+0x67/0x80
[   30.094174]  ? lockdep_hardirqs_on+0x7d/0x100
[   30.099224]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
[   30.104446] RIP: 0033:0x7f000550afbd