From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- arch/x86/hyperv/nested.c | 130 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 130 insertions(+) create mode 100644 arch/x86/hyperv/nested.c (limited to 'arch/x86/hyperv/nested.c') diff --git a/arch/x86/hyperv/nested.c b/arch/x86/hyperv/nested.c new file mode 100644 index 000000000..8ccbb7c4f --- /dev/null +++ b/arch/x86/hyperv/nested.c @@ -0,0 +1,130 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Hyper-V nested virtualization code. + * + * Copyright (C) 2018, Microsoft, Inc. + * + * Author : Lan Tianyu + */ +#define pr_fmt(fmt) "Hyper-V: " fmt + + +#include +#include +#include +#include +#include + +#include + +int hyperv_flush_guest_mapping(u64 as) +{ + struct hv_guest_mapping_flush *flush; + u64 status; + unsigned long flags; + int ret = -ENOTSUPP; + + if (!hv_hypercall_pg) + goto fault; + + local_irq_save(flags); + + flush = *this_cpu_ptr(hyperv_pcpu_input_arg); + + if (unlikely(!flush)) { + local_irq_restore(flags); + goto fault; + } + + flush->address_space = as; + flush->flags = 0; + + status = hv_do_hypercall(HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE, + flush, NULL); + local_irq_restore(flags); + + if (hv_result_success(status)) + ret = 0; + +fault: + trace_hyperv_nested_flush_guest_mapping(as, ret); + return ret; +} +EXPORT_SYMBOL_GPL(hyperv_flush_guest_mapping); + +int hyperv_fill_flush_guest_mapping_list( + struct hv_guest_mapping_flush_list *flush, + u64 start_gfn, u64 pages) +{ + u64 cur = start_gfn; + u64 additional_pages; + int gpa_n = 0; + + do { + /* + * If flush requests exceed max flush count, go back to + * flush tlbs without range. + */ + if (gpa_n >= HV_MAX_FLUSH_REP_COUNT) + return -ENOSPC; + + additional_pages = min_t(u64, pages, HV_MAX_FLUSH_PAGES) - 1; + + flush->gpa_list[gpa_n].page.additional_pages = additional_pages; + flush->gpa_list[gpa_n].page.largepage = false; + flush->gpa_list[gpa_n].page.basepfn = cur; + + pages -= additional_pages + 1; + cur += additional_pages + 1; + gpa_n++; + } while (pages > 0); + + return gpa_n; +} +EXPORT_SYMBOL_GPL(hyperv_fill_flush_guest_mapping_list); + +int hyperv_flush_guest_mapping_range(u64 as, + hyperv_fill_flush_list_func fill_flush_list_func, void *data) +{ + struct hv_guest_mapping_flush_list *flush; + u64 status; + unsigned long flags; + int ret = -ENOTSUPP; + int gpa_n = 0; + + if (!hv_hypercall_pg || !fill_flush_list_func) + goto fault; + + local_irq_save(flags); + + flush = *this_cpu_ptr(hyperv_pcpu_input_arg); + + if (unlikely(!flush)) { + local_irq_restore(flags); + goto fault; + } + + flush->address_space = as; + flush->flags = 0; + + gpa_n = fill_flush_list_func(flush, data); + if (gpa_n < 0) { + local_irq_restore(flags); + goto fault; + } + + status = hv_do_rep_hypercall(HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_LIST, + gpa_n, 0, flush, NULL); + + local_irq_restore(flags); + + if (hv_result_success(status)) + ret = 0; + else + ret = hv_result(status); +fault: + trace_hyperv_nested_flush_guest_mapping_range(as, ret); + return ret; +} +EXPORT_SYMBOL_GPL(hyperv_flush_guest_mapping_range); -- cgit v1.3.1