Apparently, cherry-picking 0828137e8f16721842468e33df0460044a0c588b
("powerpc/64s: Don't init FSCR_DSCR in __init_FSCR()") fixes the issue.
Which explains why 5.8 does not show the problem.Building a kernel with that patch applied so I can test it. Cascardo. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. 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: Triaged Status in linux source package in Eoan: Won't Fix Status in linux source package in Focal: In Progress 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 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1888332/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
