[158333.439198] x86/PAT: pcimem:922560 conflicting memory types ca000000-ca800000 uncached-minus<->write-combining

[closertotheheart]

162676.233287] x86/PAT: pcimem:978227 conflicting memory types ca000000-ca800000 uncached-minus<->write-combining
[162676.233289] x86/PAT: memtype_reserve failed [mem 0xca000000-0xca7fffff], track uncached-minus, req uncached-minus

Trying to access BAR0 of a Mellanox ConnectX-5.
Works fine on RHEL 7.7.
On RHEL it appears the BAR is mapped much higher in memory (perhaps the BIOS has the above 4G flag set)?
First time running the same logic on Ubuntu.
Running on Ubuntu produces the error.

more /sys/devices/pci0000:00/0000:00:1b.4/0000:02:00.0/resource

0x00000000ca000000 0x00000000cbffffff 0x000000000014220c
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x00000000f7100000 0x00000000f71fffff 0x0000000000046200
0x00000000ce000000 0x00000000ceffffff 0x000000000014220c
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 0x0000000000000000

02:00.0 Ethernet controller: Mellanox Technologies MT28800 Family [ConnectX-5 Ex]
Subsystem: Mellanox Technologies MT28800 Family [ConnectX-5 Ex]
Flags: bus master, fast devsel, latency 0, IRQ 16
Memory at ca000000 (64-bit, prefetchable) [size=32M]
Expansion ROM at f7100000 [disabled] [size=1M]
Capabilities: [60] Express Endpoint, MSI 00
Capabilities: [48] Vital Product Data
Capabilities: [9c] MSI-X: Enable+ Count=64 Masked-
Capabilities: [c0] Vendor Specific Information: Len=18 Capabilities: [40] Power Management version 3 Capabilities: [100] Advanced Error Reporting Capabilities: [150] Alternative Routing-ID Interpretation (ARI) Capabilities: [180] Single Root I/O Virtualization (SR-IOV) Capabilities: [1c0] Secondary PCI Express Capabilities: [230] Access Control Services Capabilities: [320] Lane Margining at the Receiver
Capabilities: [370] Physical Layer 16.0 GT/s Capabilities: [420] Data Link Feature
Kernel driver in use: mlx5_core

[closertotheheart]

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.4 LTS
Release: 20.04
Codename: focal

running on
$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 39 bits physical, 48 bits virtual
CPU(s): 12
On-line CPU(s) list: 0-11
Thread(s) per core: 2
Core(s) per socket: 6
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 158
Model name: Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
Stepping: 10
CPU MHz: 3700.000
CPU max MHz: 4900.0000
CPU min MHz: 800.0000
BogoMIPS: 7399.70
Virtualization: VT-x
L1d cache: 192 KiB
L1i cache: 192 KiB
L2 cache: 1.5 MiB
L3 cache: 12 MiB
NUMA node0 CPU(s): 0-11
Vulnerability Itlb multihit: KVM: Mitigation: VMX disabled
Vulnerability L1tf: Mitigation; PTE Inversion; VMX conditional cache flushes, SMT vulnerable
Vulnerability Mds: Mitigation; Clear CPU buffers; SMT vulnerable
Vulnerability Meltdown: Mitigation; PTI
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp
Vulnerability Spectre v1: Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2: Mitigation; Full generic retpoline, IBPB conditional, IBRS_FW, STIBP conditional, RSB filling
Vulnerability Srbds: Mitigation; Microcode
Vulnerability Tsx async abort: Mitigation; Clear CPU buffers; SMT vulnerable
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_t
sc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fau
lt epb invpcid_single pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsav
es dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp md_clear flush_l1d

$ cat /etc/redhat-release
Red Hat Enterprise Linux Server release 7.7 (Maipo)
[mrcoyle@sequoia ~]$ uname -r
3.10.0-1062.el7.x86_64

running on

$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 24
On-line CPU(s) list: 0-23
Thread(s) per core: 1
Core(s) per socket: 12
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 85
Model name: Intel(R) Xeon(R) Gold 6146 CPU @ 3.20GHz
Stepping: 4
CPU MHz: 2356.054
CPU max MHz: 4200.0000
CPU min MHz: 1200.0000
BogoMIPS: 6400.00
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 1024K
L3 cache: 25344K
NUMA node0 CPU(s): 0-11
NUMA node1 CPU(s): 12-23
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb cat_l3 cdp_l3 intel_ppin intel_pt ssbd mba ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm mpx rdt_a avx512f avx512dq rdseed adx smap clflushopt clwb avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts pku ospke md_clear spec_ctrl intel_stibp flush_l1d

[billfarrow]

I think this points to the memory already being mapped by something else, perhaps the mlx5_core driver. Have a read of Section "5.6 mmap of /dev/mem" in https://www.kernel.org/doc/ols/2008/ols2008v2-pages-135-144.pdf