From patchwork Wed Aug 18 00:12:07 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 499220 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52EFCC4338F for ; Wed, 18 Aug 2021 00:12:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A1B36109F for ; Wed, 18 Aug 2021 00:12:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237147AbhHRANE (ORCPT ); Tue, 17 Aug 2021 20:13:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237178AbhHRANC (ORCPT ); Tue, 17 Aug 2021 20:13:02 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DEEC2C061796 for ; Tue, 17 Aug 2021 17:12:28 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id n200-20020a25d6d10000b02905935ac4154aso912370ybg.23 for ; Tue, 17 Aug 2021 17:12:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=RvlRT/d0KRRmeshIggwU59tosJYpHrgSfIrmn/BlMZk=; b=J/btw2kBW8CCKgSWduzZ4yNDQ9jPCNg2xPl4jCpLAdyLiwH7QtHGV1y6kjLPOR4pVE ZDKjkdARZS8GmDTNnvP9LdXou+xjZuyTbyZJ3TuP5ICcsZkkW5Lr1qHUbtDSj4dhJzS7 ooTKH9RNJpLv9wCBmNWPbwfMvnr4qNRJXMfHRkysKURa1BJZQjPIQgg39xXByf+jp+JF e1xsDX0mNvjkbpVXPm2eN3Uirkn3K3CJ0/qSGC0uZtA8TGlRNuSxpsGKtbnjhG+il1wB wct3FluI01m6+RJVx2rqioJ+HJcc4nTCOnqLLKsHdDDCHGUYHFL0GppeRXBvO0D++aBa W50g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=RvlRT/d0KRRmeshIggwU59tosJYpHrgSfIrmn/BlMZk=; b=oxHx9cYgCwODWKVzZRh44zMYyNFEBwQm+pK64o2hyv9KwOOLiNOO2odq3Pt0UYRAaE 4LtzYFEsFYMz+D5obtOl4tKzGisTYRS6vwr9pzsxsEDTg6jIk0kqEpqEfoQeu/saAv3w 7Gq89MPSDrLEPaz6ZVZSNa3SiBhFTAmDoSkb9Y+i6iEWIXjVYtC2MDTtDMsMg2iq+mdq 5SvBIev4hAyIjA+CZKbPa5/zMhZETeppTZUBz5taLqjAVd1H+UtYxjccXcranc7MGfry sFIgMCdx/EL9nUbXl4wNkFDO2kGR6pzFXsZH7t4Cu+h84vf/zhNIW0ElU+BCOl0t9Xy4 oxdw== X-Gm-Message-State: AOAM533uzPVZR6epCaZI7mABu1npQQWzu0p2ux/vX3jOv0BYngZkgd2w zDtygRfysxu4/8cp5tVTFM5WloameOA= X-Google-Smtp-Source: ABdhPJygpO/HYN72sXYTpl6b7jRBgWVBum0X4WlFfzX7pr8xMRy0/Av5fz2lPwqaf0O3I2LLRev0nu5RwHI= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:90:200:158e:55a:74dd:5197]) (user=seanjc job=sendgmr) by 2002:a25:a369:: with SMTP id d96mr7632412ybi.463.1629245547966; Tue, 17 Aug 2021 17:12:27 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 17 Aug 2021 17:12:07 -0700 In-Reply-To: <20210818001210.4073390-1-seanjc@google.com> Message-Id: <20210818001210.4073390-3-seanjc@google.com> Mime-Version: 1.0 References: <20210818001210.4073390-1-seanjc@google.com> X-Mailer: git-send-email 2.33.0.rc1.237.g0d66db33f3-goog Subject: [PATCH 2/5] entry: rseq: Call rseq_handle_notify_resume() in tracehook_notify_resume() From: Sean Christopherson To: Russell King , Catalin Marinas , Will Deacon , Guo Ren , Thomas Bogendoerfer , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Oleg Nesterov , Steven Rostedt , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Andy Lutomirski , Mathieu Desnoyers , "Paul E. McKenney" , Boqun Feng , Paolo Bonzini , Shuah Khan Cc: Benjamin Herrenschmidt , Paul Mackerras , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Peter Foley , Shakeel Butt , Sean Christopherson , Ben Gardon Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Invoke rseq_handle_notify_resume() from tracehook_notify_resume() now that the two function are always called back-to-back by architectures that have rseq. The rseq helper is stubbed out for architectures that don't support rseq, i.e. this is a nop across the board. Note, tracehook_notify_resume() is horribly named and arguably does not belong in tracehook.h as literally every line of code in it has nothing to do with tracing. But, that's been true since commit a42c6ded827d ("move key_repace_session_keyring() into tracehook_notify_resume()") first usurped tracehook_notify_resume() back in 2012. Punt cleaning that mess up to future patches. No functional change intended. Signed-off-by: Sean Christopherson Acked-by: Mathieu Desnoyers --- arch/arm/kernel/signal.c | 1 - arch/arm64/kernel/signal.c | 1 - arch/csky/kernel/signal.c | 4 +--- arch/mips/kernel/signal.c | 4 +--- arch/powerpc/kernel/signal.c | 4 +--- arch/s390/kernel/signal.c | 1 - include/linux/tracehook.h | 2 ++ kernel/entry/common.c | 4 +--- kernel/entry/kvm.c | 4 +--- 9 files changed, 7 insertions(+), 18 deletions(-) diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c index a3a38d0a4c85..9df68d139965 100644 --- a/arch/arm/kernel/signal.c +++ b/arch/arm/kernel/signal.c @@ -670,7 +670,6 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall) uprobe_notify_resume(regs); } else { tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); } } local_irq_disable(); diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 23036334f4dc..22b55db13da6 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -951,7 +951,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, if (thread_flags & _TIF_NOTIFY_RESUME) { tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); /* * If we reschedule after checking the affinity diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c index 312f046d452d..bc4238b9f709 100644 --- a/arch/csky/kernel/signal.c +++ b/arch/csky/kernel/signal.c @@ -260,8 +260,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) do_signal(regs); - if (thread_info_flags & _TIF_NOTIFY_RESUME) { + if (thread_info_flags & _TIF_NOTIFY_RESUME) tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); - } } diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c index f1e985109da0..c9b2a75563e1 100644 --- a/arch/mips/kernel/signal.c +++ b/arch/mips/kernel/signal.c @@ -906,10 +906,8 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, void *unused, if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) do_signal(regs); - if (thread_info_flags & _TIF_NOTIFY_RESUME) { + if (thread_info_flags & _TIF_NOTIFY_RESUME) tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); - } user_enter(); } diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c index e600764a926c..b93b87df499d 100644 --- a/arch/powerpc/kernel/signal.c +++ b/arch/powerpc/kernel/signal.c @@ -293,10 +293,8 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags) do_signal(current); } - if (thread_info_flags & _TIF_NOTIFY_RESUME) { + if (thread_info_flags & _TIF_NOTIFY_RESUME) tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); - } } static unsigned long get_tm_stackpointer(struct task_struct *tsk) diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c index 78ef53b29958..b307db26bf2d 100644 --- a/arch/s390/kernel/signal.c +++ b/arch/s390/kernel/signal.c @@ -537,5 +537,4 @@ void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal) void do_notify_resume(struct pt_regs *regs) { tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); } diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h index 3e80c4bc66f7..2564b7434b4d 100644 --- a/include/linux/tracehook.h +++ b/include/linux/tracehook.h @@ -197,6 +197,8 @@ static inline void tracehook_notify_resume(struct pt_regs *regs) mem_cgroup_handle_over_high(); blkcg_maybe_throttle_current(); + + rseq_handle_notify_resume(NULL, regs); } /* diff --git a/kernel/entry/common.c b/kernel/entry/common.c index bf16395b9e13..d5a61d565ad5 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -171,10 +171,8 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) handle_signal_work(regs, ti_work); - if (ti_work & _TIF_NOTIFY_RESUME) { + if (ti_work & _TIF_NOTIFY_RESUME) tracehook_notify_resume(regs); - rseq_handle_notify_resume(NULL, regs); - } /* Architecture specific TIF work */ arch_exit_to_user_mode_work(regs, ti_work); diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c index 049fd06b4c3d..49972ee99aff 100644 --- a/kernel/entry/kvm.c +++ b/kernel/entry/kvm.c @@ -19,10 +19,8 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) if (ti_work & _TIF_NEED_RESCHED) schedule(); - if (ti_work & _TIF_NOTIFY_RESUME) { + if (ti_work & _TIF_NOTIFY_RESUME) tracehook_notify_resume(NULL); - rseq_handle_notify_resume(NULL, NULL); - } ret = arch_xfer_to_guest_mode_handle_work(vcpu, ti_work); if (ret) From patchwork Wed Aug 18 00:12:09 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 499219 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C50CDC4338F for ; Wed, 18 Aug 2021 00:12:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF1E160FD9 for ; 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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=HGsy1AYzAaNzOmCNqthC1tCvP/rp7O5tcVnL7Zz8tBI=; b=CekrMC7AADHTe8WSLDNMvdOGJWWqXjGzhXV0SQhmSfIg20iBsGJ2NlZ9nEtmvbPM3U c4b28bLcCFwNe8TgJ3PzCaZrPbK0XLSzh0Lz/jdmqxwLT6MzOw2hSmNPUUR0VC/dly56 x6TsEBJuzxp7mm0lMdveN2hkj9jU/VjhMI3f9jAMA8mvPKIHONfxiYrGft4jZZLY//AY rYB//Ngl6YsOoMTh4zS1uno6qtNfVcvLVkhC9p4ma10uRWwz3FXCXcL68a9jnJduPlgr xc/ny1x3O9qQTJKvrGDTOedyljZwyTYbHFqX54OojFI2ZGPd2Nr7SGzhc64l/765NOoR 7P/A== X-Gm-Message-State: AOAM531pv4yi2STVo1DOufU/k3r0OxSw5mjPPR21E6HAWIOsNoqGgx7b RqDqwFL8LOs6AZiRoaoOjOjfJSuJGD4= X-Google-Smtp-Source: ABdhPJxKuNoi8BurtLgbuppXh+jBMCzbufP37yZkuLi1u+HzA7x/QRXt4AsLOGUGibA7aBEUElEO9ttIYL8= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:90:200:158e:55a:74dd:5197]) (user=seanjc job=sendgmr) by 2002:a25:db82:: with SMTP id g124mr7742228ybf.46.1629245552432; Tue, 17 Aug 2021 17:12:32 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 17 Aug 2021 17:12:09 -0700 In-Reply-To: <20210818001210.4073390-1-seanjc@google.com> Message-Id: <20210818001210.4073390-5-seanjc@google.com> Mime-Version: 1.0 References: <20210818001210.4073390-1-seanjc@google.com> X-Mailer: git-send-email 2.33.0.rc1.237.g0d66db33f3-goog Subject: [PATCH 4/5] KVM: selftests: Add a test for KVM_RUN+rseq to detect task migration bugs From: Sean Christopherson To: Russell King , Catalin Marinas , Will Deacon , Guo Ren , Thomas Bogendoerfer , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Oleg Nesterov , Steven Rostedt , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Andy Lutomirski , Mathieu Desnoyers , "Paul E. McKenney" , Boqun Feng , Paolo Bonzini , Shuah Khan Cc: Benjamin Herrenschmidt , Paul Mackerras , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Peter Foley , Shakeel Butt , Sean Christopherson , Ben Gardon Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add a test to verify an rseq's CPU ID is updated correctly if the task is migrated while the kernel is handling KVM_RUN. This is a regression test for a bug introduced by commit 72c3c0fe54a3 ("x86/kvm: Use generic xfer to guest work function"), where TIF_NOTIFY_RESUME would be cleared by KVM without updating rseq, leading to a stale CPU ID and other badness. Signed-off-by: Sean Christopherson --- tools/testing/selftests/kvm/.gitignore | 1 + tools/testing/selftests/kvm/Makefile | 3 + tools/testing/selftests/kvm/rseq_test.c | 131 ++++++++++++++++++++++++ 3 files changed, 135 insertions(+) create mode 100644 tools/testing/selftests/kvm/rseq_test.c diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore index 0709af0144c8..6d031ff6b68e 100644 --- a/tools/testing/selftests/kvm/.gitignore +++ b/tools/testing/selftests/kvm/.gitignore @@ -47,6 +47,7 @@ /kvm_page_table_test /memslot_modification_stress_test /memslot_perf_test +/rseq_test /set_memory_region_test /steal_time /kvm_binary_stats_test diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile index 5832f510a16c..0756e79cb513 100644 --- a/tools/testing/selftests/kvm/Makefile +++ b/tools/testing/selftests/kvm/Makefile @@ -80,6 +80,7 @@ TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus TEST_GEN_PROGS_x86_64 += kvm_page_table_test TEST_GEN_PROGS_x86_64 += memslot_modification_stress_test TEST_GEN_PROGS_x86_64 += memslot_perf_test +TEST_GEN_PROGS_x86_64 += rseq_test TEST_GEN_PROGS_x86_64 += set_memory_region_test TEST_GEN_PROGS_x86_64 += steal_time TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test @@ -92,6 +93,7 @@ TEST_GEN_PROGS_aarch64 += dirty_log_test TEST_GEN_PROGS_aarch64 += dirty_log_perf_test TEST_GEN_PROGS_aarch64 += kvm_create_max_vcpus TEST_GEN_PROGS_aarch64 += kvm_page_table_test +TEST_GEN_PROGS_aarch64 += rseq_test TEST_GEN_PROGS_aarch64 += set_memory_region_test TEST_GEN_PROGS_aarch64 += steal_time TEST_GEN_PROGS_aarch64 += kvm_binary_stats_test @@ -103,6 +105,7 @@ TEST_GEN_PROGS_s390x += demand_paging_test TEST_GEN_PROGS_s390x += dirty_log_test TEST_GEN_PROGS_s390x += kvm_create_max_vcpus TEST_GEN_PROGS_s390x += kvm_page_table_test +TEST_GEN_PROGS_s390x += rseq_test TEST_GEN_PROGS_s390x += set_memory_region_test TEST_GEN_PROGS_s390x += kvm_binary_stats_test diff --git a/tools/testing/selftests/kvm/rseq_test.c b/tools/testing/selftests/kvm/rseq_test.c new file mode 100644 index 000000000000..90ed535eded7 --- /dev/null +++ b/tools/testing/selftests/kvm/rseq_test.c @@ -0,0 +1,131 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define _GNU_SOURCE /* for program_invocation_short_name */ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "kvm_util.h" +#include "processor.h" +#include "test_util.h" + +#define VCPU_ID 0 + +static __thread volatile struct rseq __rseq = { + .cpu_id = RSEQ_CPU_ID_UNINITIALIZED, +}; + +#define RSEQ_SIG 0xdeadbeef + +static pthread_t migration_thread; +static cpu_set_t possible_mask; +static bool done; + +static void guest_code(void) +{ + for (;;) + GUEST_SYNC(0); +} + +static void sys_rseq(int flags) +{ + int r; + + r = syscall(__NR_rseq, &__rseq, sizeof(__rseq), flags, RSEQ_SIG); + TEST_ASSERT(!r, "rseq failed, errno = %d (%s)", errno, strerror(errno)); +} + +static void *migration_worker(void *ign) +{ + cpu_set_t allowed_mask; + int r, i, nr_cpus, cpu; + + CPU_ZERO(&allowed_mask); + + nr_cpus = CPU_COUNT(&possible_mask); + + for (i = 0; i < 20000; i++) { + cpu = i % nr_cpus; + if (!CPU_ISSET(cpu, &possible_mask)) + continue; + + CPU_SET(cpu, &allowed_mask); + + r = sched_setaffinity(0, sizeof(allowed_mask), &allowed_mask); + TEST_ASSERT(!r, "sched_setaffinity failed, errno = %d (%s)", errno, + strerror(errno)); + + CPU_CLR(cpu, &allowed_mask); + + usleep(10); + } + done = true; + return NULL; +} + +int main(int argc, char *argv[]) +{ + struct kvm_vm *vm; + u32 cpu, rseq_cpu; + int r; + + /* Tell stdout not to buffer its content */ + setbuf(stdout, NULL); + + r = sched_getaffinity(0, sizeof(possible_mask), &possible_mask); + TEST_ASSERT(!r, "sched_getaffinity failed, errno = %d (%s)", errno, + strerror(errno)); + + if (CPU_COUNT(&possible_mask) < 2) { + print_skip("Only one CPU, task migration not possible\n"); + exit(KSFT_SKIP); + } + + sys_rseq(0); + + /* + * Create and run a dummy VM that immediately exits to userspace via + * GUEST_SYNC, while concurrently migrating the process by setting its + * CPU affinity. + */ + vm = vm_create_default(VCPU_ID, 0, guest_code); + + pthread_create(&migration_thread, NULL, migration_worker, 0); + + while (!done) { + vcpu_run(vm, VCPU_ID); + TEST_ASSERT(get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC, + "Guest failed?"); + + cpu = sched_getcpu(); + rseq_cpu = READ_ONCE(__rseq.cpu_id); + + /* + * Verify rseq's CPU matches sched's CPU, and that sched's CPU + * is stable. This doesn't handle the case where the task is + * migrated between sched_getcpu() and reading rseq, and again + * between reading rseq and sched_getcpu(), but in practice no + * false positives have been observed, while on the other hand + * blocking migration while this thread reads CPUs messes with + * the timing and prevents hitting failures on a buggy kernel. + */ + TEST_ASSERT(rseq_cpu == cpu || cpu != sched_getcpu(), + "rseq CPU = %d, sched CPU = %d\n", rseq_cpu, cpu); + } + + pthread_join(migration_thread, NULL); + + kvm_vm_free(vm); + + sys_rseq(RSEQ_FLAG_UNREGISTER); + + return 0; +}