When a large VM, specifically one that holds a significant number of PTEs, gets abruptly destroyed, the following warning is seen during the page-table walk: sched: CPU 0 need_resched set for > 100018840 ns (100 ticks) without schedule CPU: 0 UID: 0 PID: 9617 Comm: kvm_page_table_ Tainted: G O 6.16.0-smp-DEV #3 NONE Tainted: [O]=OOT_MODULE Call trace: show_stack+0x20/0x38 (C) dump_stack_lvl+0x3c/0xb8 dump_stack+0x18/0x30 resched_latency_warn+0x7c/0x88 sched_tick+0x1c4/0x268 update_process_times+0xa8/0xd8 tick_nohz_handler+0xc8/0x168 __hrtimer_run_queues+0x11c/0x338 hrtimer_interrupt+0x104/0x308 arch_timer_handler_phys+0x40/0x58 handle_percpu_devid_irq+0x8c/0x1b0 generic_handle_domain_irq+0x48/0x78 gic_handle_irq+0x1b8/0x408 call_on_irq_stack+0x24/0x30 do_interrupt_handler+0x54/0x78 el1_interrupt+0x44/0x88 el1h_64_irq_handler+0x18/0x28 el1h_64_irq+0x84/0x88 stage2_free_walker+0x30/0xa0 (P) __kvm_pgtable_walk+0x11c/0x258 __kvm_pgtable_walk+0x180/0x258 __kvm_pgtable_walk+0x180/0x258 __kvm_pgtable_walk+0x180/0x258 kvm_pgtable_walk+0xc4/0x140 kvm_pgtable_stage2_destroy+0x5c/0xf0 kvm_free_stage2_pgd+0x6c/0xe8 kvm_uninit_stage2_mmu+0x24/0x48 kvm_arch_flush_shadow_all+0x80/0xa0 kvm_mmu_notifier_release+0x38/0x78 __mmu_notifier_release+0x15c/0x250 exit_mmap+0x68/0x400 __mmput+0x38/0x1c8 mmput+0x30/0x68 exit_mm+0xd4/0x198 do_exit+0x1a4/0xb00 do_group_exit+0x8c/0x120 get_signal+0x6d4/0x778 do_signal+0x90/0x718 do_notify_resume+0x70/0x170 el0_svc+0x74/0xd8 el0t_64_sync_handler+0x60/0xc8 el0t_64_sync+0x1b0/0x1b8 The warning is seen majorly on the host kernels that are configured not to force-preempt, such as CONFIG_PREEMPT_NONE=y. To avoid this, instead of walking the entire page-table in one go, split it into smaller ranges, by checking for cond_resched() between each range. Since the path is executed during VM destruction, after the page-table structure is unlinked from the KVM MMU, relying on cond_resched_rwlock_write() isn't necessary. Signed-off-by: Raghavendra Rao Ananta --- arch/arm64/kvm/mmu.c | 38 ++++++++++++++++++++++++++++++++++++-- 1 file changed, 36 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 2942ec92c5a4..6c4b9fb1211b 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -387,6 +387,40 @@ static void stage2_flush_vm(struct kvm *kvm) srcu_read_unlock(&kvm->srcu, idx); } +/* + * Assume that @pgt is valid and unlinked from the KVM MMU to free the + * page-table without taking the kvm_mmu_lock and without performing any + * TLB invalidations. + * + * Also, the range of addresses can be large enough to cause need_resched + * warnings, for instance on CONFIG_PREEMPT_NONE kernels. Hence, invoke + * cond_resched() periodically to prevent hogging the CPU for a long time + * and schedule something else, if required. + */ +static void stage2_destroy_range(struct kvm_pgtable *pgt, phys_addr_t addr, + phys_addr_t end) +{ + u64 next; + + do { + next = stage2_range_addr_end(addr, end); + kvm_pgtable_stage2_destroy_range(pgt, addr, next - addr); + + if (next != end) + cond_resched(); + } while (addr = next, addr != end); +} + +static void kvm_destroy_stage2_pgt(struct kvm_pgtable *pgt) +{ + if (!is_protected_kvm_enabled()) { + stage2_destroy_range(pgt, 0, BIT(pgt->ia_bits)); + kvm_pgtable_stage2_destroy_pgd(pgt); + } else { + pkvm_pgtable_stage2_destroy(pgt); + } +} + /** * free_hyp_pgds - free Hyp-mode page tables */ @@ -984,7 +1018,7 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t return 0; out_destroy_pgtable: - KVM_PGT_FN(kvm_pgtable_stage2_destroy)(pgt); + kvm_destroy_stage2_pgt(pgt); out_free_pgtable: kfree(pgt); return err; @@ -1081,7 +1115,7 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu) write_unlock(&kvm->mmu_lock); if (pgt) { - KVM_PGT_FN(kvm_pgtable_stage2_destroy)(pgt); + kvm_destroy_stage2_pgt(pgt); kfree(pgt); } } -- 2.50.1.470.g6ba607880d-goog