From nobody Fri Jun 19 08:29:43 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 537C9C35273 for ; Tue, 5 Apr 2022 20:10:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1380431AbiDEUEk (ORCPT ); Tue, 5 Apr 2022 16:04:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1573044AbiDERsk (ORCPT ); Tue, 5 Apr 2022 13:48:40 -0400 Received: from mail-pg1-x54a.google.com (mail-pg1-x54a.google.com [IPv6:2607:f8b0:4864:20::54a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C0675D1110 for ; Tue, 5 Apr 2022 10:46:41 -0700 (PDT) Received: by mail-pg1-x54a.google.com with SMTP id b18-20020a63d812000000b0037e1aa59c0bso424pgh.12 for ; Tue, 05 Apr 2022 10:46:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=cMTfDoOyyWLXLeBs6Ru7ToFxgfyCJggJkw0OXJMsEV8=; b=nMfcorGlUtXECOW5K6EgdcUsQAcrop5tc3p5tTcoHcmFQiM5G5UW0zRhxr26er4OAr s5v6PQmrcXR71vJMJDEVfVEi6/BGDusf+GDkbu49tMPrbowlSFMgbHig8rD6DZQZmHS/ gTgnI4kYoSwt8c9IAifAu8FjUB03lSAsOwDTfv4kzBKiHU0OL9rQtUzoK2zqYD2KA11X nFbw2gOlMW++pZybJgMCWKH5eIObGH2WsSttfM4SljNf6flXef8ppdyyjRZcy6syqETb Qz+OoSYfRbFJuVp2fxQw2x7mz/1KezSRobYkumFfNg+k6O320lkst6vJRzOrzHfYxTYo fojQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=cMTfDoOyyWLXLeBs6Ru7ToFxgfyCJggJkw0OXJMsEV8=; b=tyRR/Uv0t2b8/mYPBoK7E8rgyQ2jeL26tVlgX0ZubKawS62oS1Q8ymM9Hh1yEdNRoM eqPYyyVv4zDrLV2I3yh8pYA2OWTr3eo5jdV+H7FFfiepV1as8AAYzm0LdOh8Z9caJivz dh0CUrzsZt4SnxRec4buFbCyZP9EZ/3W6o1elhYkLl69taB7v3dJpIjCNsfncNxO/Upf ws6VvNLzs2PztYe2tHF72mXosMqqL0nSRbPUizS8NPi1uVyh3H+n6dKlttqIydg/Sgsj RIESeMRBWHR/lKwAf/O848DF18XBlW81R3PtxS8DdRL/NKVgz96fzXm7dbdujRAnHanJ joOQ== X-Gm-Message-State: AOAM5330zdGDbHCKuqhubGaHxwIrniV3V7QYsCst7cFAXTnm6C4RaEXU uuRysbRsVE9mtjjNcZdm4LzSbN3aU/g= X-Google-Smtp-Source: ABdhPJyyh/3pCquJqcSiGkL89OJvx9V1mCcnl2ur+7wPBn4VOBCz5evBX3VHphcCk3xlVaHFHjDW5vPwJhk= X-Received: from pgonda1.kir.corp.google.com ([2620:15c:29:203:9f5c:353e:771c:7686]) (user=pgonda job=sendgmr) by 2002:a05:6a00:8c5:b0:4fe:134d:30d3 with SMTP id s5-20020a056a0008c500b004fe134d30d3mr4801602pfu.3.1649180801244; Tue, 05 Apr 2022 10:46:41 -0700 (PDT) Date: Tue, 5 Apr 2022 10:46:37 -0700 Message-Id: <20220405174637.2074319-1-pgonda@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.35.1.1094.g7c7d902a7c-goog Subject: [PATCH v2] KVM: SEV: Mark nested locking of vcpu->mutex From: Peter Gonda To: kvm@vger.kernel.org Cc: Peter Gonda , John Sperbeck , David Rientjes , Sean Christopherson , Paolo Bonzini , linux-kernel@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" svm_vm_migrate_from() uses sev_lock_vcpus_for_migration() to lock all source and target vcpu->mutex. Mark the nested subclasses to avoid false positives from lockdep. Warning example: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D WARNING: possible recursive locking detected 5.17.0-dbg-DEV #15 Tainted: G O Reported-by: John Sperbeck Suggested-by: David Rientjes Suggested-by: Sean Christopherson -------------------------------------------- sev_migrate_tes/18859 is trying to acquire lock: ffff8d672d484238 (&vcpu->mutex){+.+.}-{3:3}, at: sev_lock_vcpus_for_migrati= on+0x7e/0x150 but task is already holding lock: ffff8d67703f81f8 (&vcpu->mutex){+.+.}-{3:3}, at: sev_lock_vcpus_for_migrati= on+0x7e/0x150 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&vcpu->mutex); lock(&vcpu->mutex); *** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by sev_migrate_tes/18859: #0: ffff9302f91323b8 (&kvm->lock){+.+.}-{3:3}, at: sev_vm_move_enc_context= _from+0x96/0x740 #1: ffff9302f906a3b8 (&kvm->lock/1){+.+.}-{3:3}, at: sev_vm_move_enc_conte= xt_from+0xae/0x740 #2: ffff8d67703f81f8 (&vcpu->mutex){+.+.}-{3:3}, at: sev_lock_vcpus_for_mi= gration+0x7e/0x150 Fixes: b56639318bb2b ("KVM: SEV: Add support for SEV intra host migration") Reported-by: John Sperbeck Suggested-by: David Rientjes Suggested-by: Sean Christopherson Cc: Paolo Bonzini Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Peter Gonda --- Tested by running sev_migrate_tests with lockdep enabled. Before we see a warning from sev_lock_vcpus_for_migration(). After we get no warnings. --- arch/x86/kvm/svm/sev.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 75fa6dd268f0..673e1ee2cfc9 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1591,14 +1591,21 @@ static void sev_unlock_two_vms(struct kvm *dst_kvm,= struct kvm *src_kvm) atomic_set_release(&src_sev->migration_in_progress, 0); } =20 +#define SEV_MIGRATION_SOURCE 0 +#define SEV_MIGRATION_TARGET 1 =20 -static int sev_lock_vcpus_for_migration(struct kvm *kvm) +/* + * To avoid lockdep warnings callers should pass @vm argument with either + * SEV_MIGRATION_SOURCE or SEV_MIGRATE_TARGET. This allows subclassing of = all + * vCPU mutex locks. + */ +static int sev_lock_vcpus_for_migration(struct kvm *kvm, int vm) { struct kvm_vcpu *vcpu; unsigned long i, j; =20 kvm_for_each_vcpu(i, vcpu, kvm) { - if (mutex_lock_killable(&vcpu->mutex)) + if (mutex_lock_killable_nested(&vcpu->mutex, i * 2 + vm)) goto out_unlock; } =20 @@ -1745,10 +1752,10 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, u= nsigned int source_fd) charged =3D true; } =20 - ret =3D sev_lock_vcpus_for_migration(kvm); + ret =3D sev_lock_vcpus_for_migration(kvm, SEV_MIGRATION_SOURCE); if (ret) goto out_dst_cgroup; - ret =3D sev_lock_vcpus_for_migration(source_kvm); + ret =3D sev_lock_vcpus_for_migration(source_kvm, SEV_MIGRATION_TARGET); if (ret) goto out_dst_vcpu; =20 --=20 2.35.1.1094.g7c7d902a7c-goog