From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- lib/test_workqueue.c | 294 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 294 insertions(+) create mode 100644 lib/test_workqueue.c (limited to 'lib/test_workqueue.c') diff --git a/lib/test_workqueue.c b/lib/test_workqueue.c new file mode 100644 index 000000000..2bdfcbbca --- /dev/null +++ b/lib/test_workqueue.c @@ -0,0 +1,294 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Test module for stress and performance analysis of workqueue. + * + * Benchmarks queue_work() throughput on an unbound workqueue to measure + * pool->lock contention under different affinity scope configurations + * (e.g., cache vs cache_shard). + * + * The affinity scope is changed between runs via the workqueue's sysfs + * affinity_scope attribute (WQ_SYSFS). + * + * Copyright (c) 2026 Meta Platforms, Inc. and affiliates + * Copyright (c) 2026 Breno Leitao + * + */ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define WQ_NAME "bench_wq" +#define SCOPE_PATH "/sys/bus/workqueue/devices/" WQ_NAME "/affinity_scope" + +static int nr_threads; +module_param(nr_threads, int, 0444); +MODULE_PARM_DESC(nr_threads, + "Number of threads to spawn (default: 0 = num_online_cpus())"); + +static int wq_items = 50000; +module_param(wq_items, int, 0444); +MODULE_PARM_DESC(wq_items, + "Number of work items each thread queues (default: 50000)"); + +static struct workqueue_struct *bench_wq; +static atomic_t threads_done; +static DECLARE_COMPLETION(start_comp); +static DECLARE_COMPLETION(all_done_comp); + +struct thread_ctx { + struct completion work_done; + struct work_struct work; + u64 *latencies; + int cpu; + int items; +}; + +static void bench_work_fn(struct work_struct *work) +{ + struct thread_ctx *ctx = container_of(work, struct thread_ctx, work); + + complete(&ctx->work_done); +} + +static int bench_kthread_fn(void *data) +{ + struct thread_ctx *ctx = data; + ktime_t t_start, t_end; + int i; + + /* Wait for all threads to be ready */ + wait_for_completion(&start_comp); + + if (kthread_should_stop()) + return 0; + + for (i = 0; i < ctx->items; i++) { + reinit_completion(&ctx->work_done); + INIT_WORK(&ctx->work, bench_work_fn); + + t_start = ktime_get(); + queue_work(bench_wq, &ctx->work); + t_end = ktime_get(); + + ctx->latencies[i] = ktime_to_ns(ktime_sub(t_end, t_start)); + wait_for_completion(&ctx->work_done); + } + + if (atomic_dec_and_test(&threads_done)) + complete(&all_done_comp); + + /* + * Wait for kthread_stop() so the module text isn't freed + * while we're still executing. + */ + while (!kthread_should_stop()) + schedule(); + + return 0; +} + +static int cmp_u64(const void *a, const void *b) +{ + u64 va = *(const u64 *)a; + u64 vb = *(const u64 *)b; + + if (va < vb) + return -1; + if (va > vb) + return 1; + return 0; +} + +static int __init set_affn_scope(const char *scope) +{ + struct file *f; + loff_t pos = 0; + ssize_t ret; + + f = filp_open(SCOPE_PATH, O_WRONLY, 0); + if (IS_ERR(f)) { + pr_err("test_workqueue: open %s failed: %ld\n", + SCOPE_PATH, PTR_ERR(f)); + return PTR_ERR(f); + } + + ret = kernel_write(f, scope, strlen(scope), &pos); + filp_close(f, NULL); + + if (ret < 0) { + pr_err("test_workqueue: write '%s' failed: %zd\n", scope, ret); + return ret; + } + + return 0; +} + +static int __init run_bench(int n_threads, const char *scope, const char *label) +{ + struct task_struct **tasks; + unsigned long total_items; + struct thread_ctx *ctxs; + u64 *all_latencies; + ktime_t start, end; + int cpu, i, j, ret; + s64 elapsed_us; + + ret = set_affn_scope(scope); + if (ret) + return ret; + + ctxs = kzalloc_objs(*ctxs, n_threads); + if (!ctxs) + return -ENOMEM; + + tasks = kzalloc_objs(*tasks, n_threads); + if (!tasks) { + kfree(ctxs); + return -ENOMEM; + } + + total_items = (unsigned long)n_threads * wq_items; + all_latencies = kvmalloc_array(total_items, sizeof(u64), GFP_KERNEL); + if (!all_latencies) { + kfree(tasks); + kfree(ctxs); + return -ENOMEM; + } + + /* Allocate per-thread latency arrays */ + for (i = 0; i < n_threads; i++) { + ctxs[i].latencies = kvmalloc_array(wq_items, sizeof(u64), + GFP_KERNEL); + if (!ctxs[i].latencies) { + while (--i >= 0) + kvfree(ctxs[i].latencies); + kvfree(all_latencies); + kfree(tasks); + kfree(ctxs); + return -ENOMEM; + } + } + + atomic_set(&threads_done, n_threads); + reinit_completion(&all_done_comp); + reinit_completion(&start_comp); + + /* Create kthreads, each bound to a different online CPU */ + i = 0; + for_each_online_cpu(cpu) { + if (i >= n_threads) + break; + + ctxs[i].cpu = cpu; + ctxs[i].items = wq_items; + init_completion(&ctxs[i].work_done); + + tasks[i] = kthread_create(bench_kthread_fn, &ctxs[i], + "wq_bench/%d", cpu); + if (IS_ERR(tasks[i])) { + ret = PTR_ERR(tasks[i]); + pr_err("test_workqueue: failed to create kthread %d: %d\n", + i, ret); + /* Unblock threads waiting on start_comp before stopping them */ + complete_all(&start_comp); + while (--i >= 0) + kthread_stop(tasks[i]); + goto out_free; + } + + kthread_bind(tasks[i], cpu); + wake_up_process(tasks[i]); + i++; + } + + /* Start timing and release all threads */ + start = ktime_get(); + complete_all(&start_comp); + + /* Wait for all threads to finish the benchmark */ + wait_for_completion(&all_done_comp); + + /* Drain any remaining work */ + flush_workqueue(bench_wq); + + /* Ensure all kthreads have fully exited before module memory is freed */ + for (i = 0; i < n_threads; i++) + kthread_stop(tasks[i]); + + end = ktime_get(); + elapsed_us = ktime_us_delta(end, start); + + /* Merge all per-thread latencies and sort for percentile calculation */ + j = 0; + for (i = 0; i < n_threads; i++) { + memcpy(&all_latencies[j], ctxs[i].latencies, + wq_items * sizeof(u64)); + j += wq_items; + } + + sort(all_latencies, total_items, sizeof(u64), cmp_u64, NULL); + + pr_info("test_workqueue: %-16s %llu items/sec\tp50=%llu\tp90=%llu\tp95=%llu ns\n", + label, + elapsed_us ? div_u64(total_items * 1000000ULL, elapsed_us) : 0, + all_latencies[total_items * 50 / 100], + all_latencies[total_items * 90 / 100], + all_latencies[total_items * 95 / 100]); + + ret = 0; +out_free: + for (i = 0; i < n_threads; i++) + kvfree(ctxs[i].latencies); + kvfree(all_latencies); + kfree(tasks); + kfree(ctxs); + + return ret; +} + +static const char * const bench_scopes[] = { + "cpu", "smt", "cache_shard", "cache", "numa", "system", +}; + +static int __init test_workqueue_init(void) +{ + int n_threads = min(nr_threads ?: num_online_cpus(), num_online_cpus()); + int i; + + if (wq_items <= 0) { + pr_err("test_workqueue: wq_items must be > 0\n"); + return -EINVAL; + } + + bench_wq = alloc_workqueue(WQ_NAME, WQ_UNBOUND | WQ_SYSFS, 0); + if (!bench_wq) + return -ENOMEM; + + pr_info("test_workqueue: running %d threads, %d items/thread\n", + n_threads, wq_items); + + for (i = 0; i < ARRAY_SIZE(bench_scopes); i++) + run_bench(n_threads, bench_scopes[i], bench_scopes[i]); + + destroy_workqueue(bench_wq); + + /* Return -EAGAIN so the module doesn't stay loaded after the benchmark */ + return -EAGAIN; +} + +module_init(test_workqueue_init); +MODULE_AUTHOR("Breno Leitao "); +MODULE_DESCRIPTION("Stress/performance benchmark for workqueue subsystem"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1