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07bf9431b1
Sachin reported [1] that on a POWER-10 lpar he is seeing a kernel panic being
reported with vPMEM when papr_scm probe is being called. The panic is of the
form below and is observed only with following option disabled(profile) for the
said LPAR 'Enable Performance Information Collection' in the HMC:
Kernel attempted to write user page (1c) - exploit attempt? (uid: 0)
BUG: Kernel NULL pointer dereference on write at 0x0000001c
Faulting instruction address: 0xc008000001b90844
Oops: Kernel access of bad area, sig: 11 [#1]
<snip>
NIP [c008000001b90844] drc_pmem_query_stats+0x5c/0x270 [papr_scm]
LR [c008000001b92794] papr_scm_probe+0x2ac/0x6ec [papr_scm]
Call Trace:
0xc00000000941bca0 (unreliable)
papr_scm_probe+0x2ac/0x6ec [papr_scm]
platform_probe+0x98/0x150
really_probe+0xfc/0x510
__driver_probe_device+0x17c/0x230
<snip>
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Fatal exception
On investigation looks like this panic was caused due to a 'stat_buffer' of
size==0 being provided to drc_pmem_query_stats() to fetch all performance
stats-ids of an NVDIMM. However drc_pmem_query_stats() shouldn't have been called
since the vPMEM NVDIMM doesn't support and performance stat-id's. This was caused
due to missing check for 'p->stat_buffer_len' at the beginning of
papr_scm_pmu_check_events() which indicates that the NVDIMM doesn't support
performance-stats.
Fix this by introducing the check for 'p->stat_buffer_len' at the beginning of
papr_scm_pmu_check_events().
[1] https://lore.kernel.org/all/6B3A522A-6A5F-4CC9-B268-0C63AA6E07D3@linux.ibm.com
Fixes:
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History
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.