[PATCH 0/1] [SRU][F/G][RISCV] riscv: set max_pfn to the PFN of the last page

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

[ For ubuntu-riscv-focal ubuntu-riscv-groovy ]

BugLink: https://bugs.launchpad.net/bugs/1876885

== 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 <vincent.chen at sifive.com>
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.

Vincent Chen (1):
  riscv: set max_pfn to the PFN of the last page

 arch/riscv/mm/init.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

-- 
2.25.1