** Changed in: linux (Ubuntu Focal)
Status: In Progress => Fix Committed
** Changed in: linux (Ubuntu Focal)
Importance: Undecided => High
** Changed in: linux (Ubuntu Focal)
Importance: High => Medium
** Changed in: linux (Ubuntu Bionic)
Importance: Undecided => Medium
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https://bugs.launchpad.net/bugs/1888332
Title:
[Potential Regression] dscr_inherit_exec_test from powerpc in
ubuntu_kernel_selftests failed on B/E/F
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Bionic:
In Progress
Status in linux source package in Eoan:
Won't Fix
Status in linux source package in Focal:
Fix Committed
Bug description:
[Impact]
Code that touches DSCR user MSR does not set dscr_inherit, which breaks DSCR
restore doing context switches and inheritance when forking. DSCR is used to
control cache hinting. This is caused by lack of kernel interrupt when the DSCR
user MSR is written, which is controlled by FSCR which would otherwise cause a
facility unavailable interrupt.
[Test case]
apt-get source linux
cd linux-5.4.0/tools/testing/tools/selftests/powerpc/
make -j 32
make -C dscr run_tests
make -C ptrace run_tests
make -C tm run_tests
Look up for "not ok" versus "ok", specially for
dscr_inherit_exec_test, ptrace-tar and tm-resched-tar.
[Potential regression]
Manipulating DSCR might break on different machines (with DTs containing
/cpus/ibm,powerpc-cpu-features, for example). Code that does so might crash
because the facility unavailable interrupt handling might be not working
correctly.
====================================
Issue found on 5.3.0-64.58 with P8 node modoc (passed with P9 node)
# selftests: powerpc/dscr: dscr_inherit_exec_test
# test: dscr_inherit_exec_test
# tags: git_version:unknown
# Parent DSCR 1 was not inherited over exec (kernel value)
# Child didn't exit cleanly
# failure: dscr_inherit_exec_test
not ok 5 selftests: powerpc/dscr: dscr_inherit_exec_test # exit=1
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