user/sven/linux.git/kernel/cpu.c, branch v4.14.112

cpu/hotplug: Mute hotplug lockdep during init

2019-04-05T20:31:38Z

[ Upstream commit ce48c457b95316b9a01b5aa9d4456ce820df94b4 ] Since we've had: commit cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations") we've been getting some lockdep warnings during init, such as on HiKey960: [ 0.820495] WARNING: CPU: 4 PID: 0 at kernel/cpu.c:316 lockdep_assert_cpus_held+0x3c/0x48 [ 0.820498] Modules linked in: [ 0.820509] CPU: 4 PID: 0 Comm: swapper/4 Tainted: G S 4.20.0-rc5-00051-g4cae42a #34 [ 0.820511] Hardware name: HiKey960 (DT) [ 0.820516] pstate: 600001c5 (nZCv dAIF -PAN -UAO) [ 0.820520] pc : lockdep_assert_cpus_held+0x3c/0x48 [ 0.820523] lr : lockdep_assert_cpus_held+0x38/0x48 [ 0.820526] sp : ffff00000a9cbe50 [ 0.820528] x29: ffff00000a9cbe50 x28: 0000000000000000 [ 0.820533] x27: 00008000b69e5000 x26: ffff8000bff4cfe0 [ 0.820537] x25: ffff000008ba69e0 x24: 0000000000000001 [ 0.820541] x23: ffff000008fce000 x22: ffff000008ba70c8 [ 0.820545] x21: 0000000000000001 x20: 0000000000000003 [ 0.820548] x19: ffff00000a35d628 x18: ffffffffffffffff [ 0.820552] x17: 0000000000000000 x16: 0000000000000000 [ 0.820556] x15: ffff00000958f848 x14: 455f3052464d4d34 [ 0.820559] x13: 00000000769dde98 x12: ffff8000bf3f65a8 [ 0.820564] x11: 0000000000000000 x10: ffff00000958f848 [ 0.820567] x9 : ffff000009592000 x8 : ffff00000958f848 [ 0.820571] x7 : ffff00000818ffa0 x6 : 0000000000000000 [ 0.820574] x5 : 0000000000000000 x4 : 0000000000000001 [ 0.820578] x3 : 0000000000000000 x2 : 0000000000000001 [ 0.820582] x1 : 00000000ffffffff x0 : 0000000000000000 [ 0.820587] Call trace: [ 0.820591] lockdep_assert_cpus_held+0x3c/0x48 [ 0.820598] static_key_enable_cpuslocked+0x28/0xd0 [ 0.820606] arch_timer_check_ool_workaround+0xe8/0x228 [ 0.820610] arch_timer_starting_cpu+0xe4/0x2d8 [ 0.820615] cpuhp_invoke_callback+0xe8/0xd08 [ 0.820619] notify_cpu_starting+0x80/0xb8 [ 0.820625] secondary_start_kernel+0x118/0x1d0 We've also had a similar warning in sched_init_smp() for every asymmetric system that would enable the sched_asym_cpucapacity static key, although that was singled out in: commit 40fa3780bac2 ("sched/core: Take the hotplug lock in sched_init_smp()") Those warnings are actually harmless, since we cannot have hotplug operations at the time they appear. Instead of starting to sprinkle useless hotplug lock operations in the init codepaths, mute the warnings until they start warning about real problems. Suggested-by: Peter Zijlstra Signed-off-by: Valentin Schneider Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Thomas Gleixner Cc: Will Deacon Cc: cai@gmx.us Cc: daniel.lezcano@linaro.org Cc: dietmar.eggemann@arm.com Cc: linux-arm-kernel@lists.infradead.org Cc: longman@redhat.com Cc: marc.zyngier@arm.com Cc: mark.rutland@arm.com Link: https://lkml.kernel.org/r/1545243796-23224-2-git-send-email-valentin.schneider@arm.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

cpu/hotplug: Prevent crash when CPU bringup fails on CONFIG_HOTPLUG_CPU=n

2019-04-03T04:25:20Z

commit 206b92353c839c0b27a0b9bec24195f93fd6cf7a upstream. Tianyu reported a crash in a CPU hotplug teardown callback when booting a kernel which has CONFIG_HOTPLUG_CPU disabled with the 'nosmt' boot parameter. It turns out that the SMP=y CONFIG_HOTPLUG_CPU=n case has been broken forever in case that a bringup callback fails. Unfortunately this issue was not recognized when the CPU hotplug code was reworked, so the shortcoming just stayed in place. When a bringup callback fails, the CPU hotplug code rolls back the operation and takes the CPU offline. The 'nosmt' command line argument uses a bringup failure to abort the bringup of SMT sibling CPUs. This partial bringup is required due to the MCE misdesign on Intel CPUs. With CONFIG_HOTPLUG_CPU=y the rollback works perfectly fine, but CONFIG_HOTPLUG_CPU=n lacks essential mechanisms to exercise the low level teardown of a CPU including the synchronizations in various facilities like RCU, NOHZ and others. As a consequence the teardown callbacks which must be executed on the outgoing CPU within stop machine with interrupts disabled are executed on the control CPU in interrupt enabled and preemptible context causing the kernel to crash and burn. The pre state machine code has a different failure mode which is more subtle and resulting in a less obvious use after free crash because the control side frees resources which are still in use by the undead CPU. But this is not a x86 only problem. Any architecture which supports the SMP=y HOTPLUG_CPU=n combination suffers from the same issue. It's just less likely to be triggered because in 99.99999% of the cases all bringup callbacks succeed. The easy solution of making HOTPLUG_CPU mandatory for SMP is not working on all architectures as the following architectures have either no hotplug support at all or not all subarchitectures support it: alpha, arc, hexagon, openrisc, riscv, sparc (32bit), mips (partial). Crashing the kernel in such a situation is not an acceptable state either. Implement a minimal rollback variant by limiting the teardown to the point where all regular teardown callbacks have been invoked and leave the CPU in the 'dead' idle state. This has the following consequences: - the CPU is brought down to the point where the stop_machine takedown would happen. - the CPU stays there forever and is idle - The CPU is cleared in the CPU active mask, but not in the CPU online mask which is a legit state. - Interrupts are not forced away from the CPU - All facilities which only look at online mask would still see it, but that is the case during normal hotplug/unplug operations as well. It's just a (way) longer time frame. This will expose issues, which haven't been exposed before or only seldom, because now the normally transient state of being non active but online is a permanent state. In testing this exposed already an issue vs. work queues where the vmstat code schedules work on the almost dead CPU which ends up in an unbound workqueue and triggers 'preemtible context' warnings. This is not a problem of this change, it merily exposes an already existing issue. Still this is better than crashing fully without a chance to debug it. This is mainly thought as workaround for those architectures which do not support HOTPLUG_CPU. All others should enforce HOTPLUG_CPU for SMP. Fixes: 2e1a3483ce74 ("cpu/hotplug: Split out the state walk into functions") Reported-by: Tianyu Lan Signed-off-by: Thomas Gleixner Tested-by: Tianyu Lan Acked-by: Greg Kroah-Hartman Cc: Konrad Wilk Cc: Josh Poimboeuf Cc: Mukesh Ojha Cc: Peter Zijlstra Cc: Jiri Kosina Cc: Rik van Riel Cc: Andy Lutomirski Cc: Micheal Kelley Cc: "K. Y. Srinivasan" Cc: Linus Torvalds Cc: Borislav Petkov Cc: K. Y. Srinivasan Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20190326163811.503390616@linutronix.de Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVM

2019-02-12T18:46:13Z

commit b284909abad48b07d3071a9fc9b5692b3e64914b upstream. With the following commit: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") ... the hotplug code attempted to detect when SMT was disabled by BIOS, in which case it reported SMT as permanently disabled. However, that code broke a virt hotplug scenario, where the guest is booted with only primary CPU threads, and a sibling is brought online later. The problem is that there doesn't seem to be a way to reliably distinguish between the HW "SMT disabled by BIOS" case and the virt "sibling not yet brought online" case. So the above-mentioned commit was a bit misguided, as it permanently disabled SMT for both cases, preventing future virt sibling hotplugs. Going back and reviewing the original problems which were attempted to be solved by that commit, when SMT was disabled in BIOS: 1) /sys/devices/system/cpu/smt/control showed "on" instead of "notsupported"; and 2) vmx_vm_init() was incorrectly showing the L1TF_MSG_SMT warning. I'd propose that we instead consider #1 above to not actually be a problem. Because, at least in the virt case, it's possible that SMT wasn't disabled by BIOS and a sibling thread could be brought online later. So it makes sense to just always default the smt control to "on" to allow for that possibility (assuming cpuid indicates that the CPU supports SMT). The real problem is #2, which has a simple fix: change vmx_vm_init() to query the actual current SMT state -- i.e., whether any siblings are currently online -- instead of looking at the SMT "control" sysfs value. So fix it by: a) reverting the original "fix" and its followup fix: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") bc2d8d262cba ("cpu/hotplug: Fix SMT supported evaluation") and b) changing vmx_vm_init() to query the actual current SMT state -- instead of the sysfs control value -- to determine whether the L1TF warning is needed. This also requires the 'sched_smt_present' variable to exported, instead of 'cpu_smt_control'. Fixes: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") Reported-by: Igor Mammedov Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Cc: Joe Mario Cc: Jiri Kosina Cc: Peter Zijlstra Cc: kvm@vger.kernel.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/e3a85d585da28cc333ecbc1e78ee9216e6da9396.1548794349.git.jpoimboe@redhat.com Signed-off-by: Greg Kroah-Hartman

x86/speculation: Rework SMT state change

2018-12-05T18:41:20Z

commit a74cfffb03b73d41e08f84c2e5c87dec0ce3db9f upstream arch_smt_update() is only called when the sysfs SMT control knob is changed. This means that when SMT is enabled in the sysfs control knob the system is considered to have SMT active even if all siblings are offline. To allow finegrained control of the speculation mitigations, the actual SMT state is more interesting than the fact that siblings could be enabled. Rework the code, so arch_smt_update() is invoked from each individual CPU hotplug function, and simplify the update function while at it. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Jiri Kosina Cc: Tom Lendacky Cc: Josh Poimboeuf Cc: Andrea Arcangeli Cc: David Woodhouse Cc: Tim Chen Cc: Andi Kleen Cc: Dave Hansen Cc: Casey Schaufler Cc: Asit Mallick Cc: Arjan van de Ven Cc: Jon Masters Cc: Waiman Long Cc: Greg KH Cc: Dave Stewart Cc: Kees Cook Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181125185004.521974984@linutronix.de Signed-off-by: Greg Kroah-Hartman

x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

2018-12-05T18:41:18Z

commit 53c613fe6349994f023245519265999eed75957f upstream STIBP is a feature provided by certain Intel ucodes / CPUs. This feature (once enabled) prevents cross-hyperthread control of decisions made by indirect branch predictors. Enable this feature if - the CPU is vulnerable to spectre v2 - the CPU supports SMT and has SMT siblings online - spectre_v2 mitigation autoselection is enabled (default) After some previous discussion, this leaves STIBP on all the time, as wrmsr on crossing kernel boundary is a no-no. This could perhaps later be a bit more optimized (like disabling it in NOHZ, experiment with disabling it in idle, etc) if needed. Note that the synchronization of the mask manipulation via newly added spec_ctrl_mutex is currently not strictly needed, as the only updater is already being serialized by cpu_add_remove_lock, but let's make this a little bit more future-proof. Signed-off-by: Jiri Kosina Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Andrea Arcangeli Cc: "WoodhouseDavid" Cc: Andi Kleen Cc: Tim Chen Cc: "SchauflerCasey" Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251438240.15880@cbobk.fhfr.pm Signed-off-by: Greg Kroah-Hartman

Revert "x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation"

2018-11-23T07:19:27Z

This reverts commit 8a13906ae519b3ed95cd0fb73f1098b46362f6c4 which is commit 53c613fe6349994f023245519265999eed75957f upstream. It's not ready for the stable trees as there are major slowdowns involved with this patch. Reported-by: Jiri Kosina Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Andrea Arcangeli Cc: "WoodhouseDavid" Cc: Andi Kleen Cc: Tim Chen Cc: "SchauflerCasey" Signed-off-by: Greg Kroah-Hartman

x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

2018-11-13T19:14:47Z

commit 53c613fe6349994f023245519265999eed75957f upstream. STIBP is a feature provided by certain Intel ucodes / CPUs. This feature (once enabled) prevents cross-hyperthread control of decisions made by indirect branch predictors. Enable this feature if - the CPU is vulnerable to spectre v2 - the CPU supports SMT and has SMT siblings online - spectre_v2 mitigation autoselection is enabled (default) After some previous discussion, this leaves STIBP on all the time, as wrmsr on crossing kernel boundary is a no-no. This could perhaps later be a bit more optimized (like disabling it in NOHZ, experiment with disabling it in idle, etc) if needed. Note that the synchronization of the mask manipulation via newly added spec_ctrl_mutex is currently not strictly needed, as the only updater is already being serialized by cpu_add_remove_lock, but let's make this a little bit more future-proof. Signed-off-by: Jiri Kosina Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Andrea Arcangeli Cc: "WoodhouseDavid" Cc: Andi Kleen Cc: Tim Chen Cc: "SchauflerCasey" Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251438240.15880@cbobk.fhfr.pm Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Prevent state corruption on error rollback

2018-09-19T20:43:36Z

commit 69fa6eb7d6a64801ea261025cce9723d9442d773 upstream. When a teardown callback fails, the CPU hotplug code brings the CPU back to the previous state. The previous state becomes the new target state. The rollback happens in undo_cpu_down() which increments the state unconditionally even if the state is already the same as the target. As a consequence the next CPU hotplug operation will start at the wrong state. This is easily to observe when __cpu_disable() fails. Prevent the unconditional undo by checking the state vs. target before incrementing state and fix up the consequently wrong conditional in the unplug code which handles the failure of the final CPU take down on the control CPU side. Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core") Reported-by: Neeraj Upadhyay Signed-off-by: Thomas Gleixner Tested-by: Geert Uytterhoeven Tested-by: Sudeep Holla Tested-by: Neeraj Upadhyay Cc: josh@joshtriplett.org Cc: peterz@infradead.org Cc: jiangshanlai@gmail.com Cc: dzickus@redhat.com Cc: brendan.jackman@arm.com Cc: malat@debian.org Cc: sramana@codeaurora.org Cc: linux-arm-msm@vger.kernel.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1809051419580.1416@nanos.tec.linutronix.de Signed-off-by: Greg Kroah-Hartman ----

cpu/hotplug: Adjust misplaced smb() in cpuhp_thread_fun()

2018-09-19T20:43:36Z

commit f8b7530aa0a1def79c93101216b5b17cf408a70a upstream. The smp_mb() in cpuhp_thread_fun() is misplaced. It needs to be after the load of st->should_run to prevent reordering of the later load/stores w.r.t. the load of st->should_run. Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core") Signed-off-by: Neeraj Upadhyay Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra (Intel) Cc: josh@joshtriplett.org Cc: peterz@infradead.org Cc: jiangshanlai@gmail.com Cc: dzickus@redhat.com Cc: brendan.jackman@arm.com Cc: malat@debian.org Cc: mojha@codeaurora.org Cc: sramana@codeaurora.org Cc: linux-arm-msm@vger.kernel.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/1536126727-11629-1-git-send-email-neeraju@codeaurora.org Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Non-SMP machines do not make use of booted_once

2018-08-15T16:13:01Z

commit 269777aa530f3438ec1781586cdac0b5fe47b061 upstream. Commit 0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once") breaks non-SMP builds. [ I suspect the 'bool' fields should just be made to be bitfields and be exposed regardless of configuration, but that's a separate cleanup that I'll leave to the owners of this file for later. - Linus ] Fixes: 0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once") Cc: Dave Hansen Cc: Thomas Gleixner Cc: Tony Luck Signed-off-by: Abel Vesa Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman