Hello! This series is continuation of main core-sched v6 series [1] and adds support for syscall and IRQ isolation from usermode processes and guests. It is key to safely entering kernel mode in an HT while the other HT is in use by a user or guest. The series also fixes CPU hotplug issues arising because of the cpu_smt_mask changing while the next task is being picked. These hotplug fixes are needed also for kernel protection to work correctly.
The series is based on Thomas's x86/entry tree. [1] https://lwn.net/Articles/824918/ Background: Core-scheduling prevents hyperthreads in usermode from attacking each other, but it does not do anything about one of the hyperthreads entering the kernel for any reason. This leaves the door open for MDS and L1TF attacks with concurrent execution sequences between hyperthreads. This series adds support for protecting all syscall and IRQ kernel mode entries by cleverly tracking when any sibling in a core enter the kernel, and when all the siblings exit the kernel. IPIs are sent to force siblings into the kernel. Care is taken to avoid waiting in IRQ-disabled sections as Thomas suggested thus avoiding stop_machine deadlocks. Every attempt is made to avoid unnecessary IPIs. Performance tests: sysbench is used to test the performance of the patch series. Used a 8 cpu/4 Core VM and ran 2 sysbench tests in parallel. Each sysbench test runs 4 tasks: sysbench --test=cpu --cpu-max-prime=100000 --num-threads=4 run Compared the performance results for various combinations as below. The metric below is 'events per second': 1. Coresched disabled sysbench-1/sysbench-2 => 175.7/175.6 2. Coreched enabled, both sysbench tagged sysbench-1/sysbench-2 => 168.8/165.6 3. Coresched enabled, sysbench-1 tagged and sysbench-2 untagged sysbench-1/sysbench-2 => 96.4/176.9 4. smt off sysbench-1/sysbench-2 => 97.9/98.8 When both sysbench-es are tagged, there is a perf drop of ~4%. With a tagged/untagged case, the tagged one suffers because it always gets stalled when the sibiling enters kernel. But this is no worse than smtoff. Also a modified rcutorture was used to heavily stress the kernel to make sure there is not crash or instability. Joel Fernandes (Google) (5): irq_work: Add support to detect if work is pending entry/idle: Add a common function for activites during idle entry/exit arch/x86: Add a new TIF flag for untrusted tasks kernel/entry: Add support for core-wide protection of kernel-mode entry/idle: Enter and exit kernel protection during idle entry and exit Vineeth Pillai (7): entry/kvm: Protect the kernel when entering from guest bitops: Introduce find_next_or_bit cpumask: Introduce a new iterator for_each_cpu_wrap_or sched/coresched: Use for_each_cpu(_wrap)_or for pick_next_task sched/coresched: Make core_pick_seq per run-queue sched/coresched: Check for dynamic changes in smt_mask sched/coresched: rq->core should be set only if not previously set arch/x86/include/asm/thread_info.h | 2 + arch/x86/kvm/x86.c | 3 + include/asm-generic/bitops/find.h | 16 ++ include/linux/cpumask.h | 42 +++++ include/linux/entry-common.h | 22 +++ include/linux/entry-kvm.h | 12 ++ include/linux/irq_work.h | 1 + include/linux/sched.h | 12 ++ kernel/entry/common.c | 88 +++++---- kernel/entry/kvm.c | 12 ++ kernel/irq_work.c | 11 ++ kernel/sched/core.c | 281 ++++++++++++++++++++++++++--- kernel/sched/idle.c | 17 +- kernel/sched/sched.h | 11 +- lib/cpumask.c | 53 ++++++ lib/find_bit.c | 56 ++++-- 16 files changed, 564 insertions(+), 75 deletions(-) -- 2.28.0.220.ged08abb693-goog