** Also affects: linux (Ubuntu Focal)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Focal)
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1876885
Title:
linux: riscv: set max_pfn to the PFN of the last page
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Focal:
Fix Committed
Bug description:
== SRU Justification Focal/Groovy ==
The current max_pfn equals to zero. In this case, I found it caused users
cannot get some page information through /proc such as kpagecount in v5.6
kernel because of new sanity checks. The following message is displayed by
stress-ng test suite with the command "stress-ng --verbose --physpage 1 -t
1" on HiFive unleashed board.
# stress-ng --verbose --physpage 1 -t 1
stress-ng: debug: [109] 4 processors online, 4 processors configured
stress-ng: info: [109] dispatching hogs: 1 physpage
stress-ng: debug: [109] cache allocate: reducing cache level from L3 (too
high) to L0
stress-ng: debug: [109] get_cpu_cache: invalid cache_level: 0
stress-ng: info: [109] cache allocate: using built-in defaults as no
suitable cache found
stress-ng: debug: [109] cache allocate: default cache size: 2048K
stress-ng: debug: [109] starting stressors
stress-ng: debug: [109] 1 stressor spawned
stress-ng: debug: [110] stress-ng-physpage: started [110] (instance 0)
stress-ng: error: [110] stress-ng-physpage: cannot read page count for
address 0x3fd34de000 in /proc/kpagecount, errno=0 (Success)
stress-ng: error: [110] stress-ng-physpage: cannot read page count for
address 0x3fd32db078 in /proc/kpagecount, errno=0 (Success)
...
stress-ng: error: [110] stress-ng-physpage: cannot read page count for
address 0x3fd32db078 in /proc/kpagecount, errno=0 (Success)
stress-ng: debug: [110] stress-ng-physpage: exited [110] (instance 0)
stress-ng: debug: [109] process [110] terminated
stress-ng: info: [109] successful run completed in 1.00s
#
== Fix ==
Upstream commit in linux-next:
commit c749bb2d554825e007cbc43b791f54e124dadfce
Author: Vincent Chen <[email protected]>
Date: Mon Apr 27 14:59:24 2020 +0800
riscv: set max_pfn to the PFN of the last page
== Test Case ==
Without the patch, running stress-ng --verbose --physpage 1 -t
1 on HiFive unleashed board will trip the bug. With the patch, the test
passes as follows:
# stress-ng --verbose --physpage 1 -t 1
stress-ng: debug: [104] 4 processors online, 4 processors configured
stress-ng: info: [104] dispatching hogs: 1 physpage
stress-ng: info: [104] cache allocate: using defaults, can't determine cache
details from sysfs
stress-ng: debug: [104] cache allocate: default cache size: 2048K
stress-ng: debug: [104] starting stressors
stress-ng: debug: [104] 1 stressor spawned
stress-ng: debug: [105] stress-ng-physpage: started [105] (instance 0)
stress-ng: debug: [105] stress-ng-physpage: exited [105] (instance 0)
stress-ng: debug: [104] process [105] terminated
stress-ng: info: [104] successful run completed in 1.01s
== Regression Potential ==
Small, this correctly fixes the max_pfn and max_low_pfn to the correct
end of DRAM location. The fix now can be shown to set these
appropriately because stress-ng no longer triggers this corner case.
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