From patchwork Fri Jan 24 23:46:23 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13950020 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75C461E7C3D for ; Fri, 24 Jan 2025 23:47:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737762426; cv=none; b=dDQT5p6l8vEThkpYQpumdMwxcIgqEwPsGuSZ9HOMQerKHcq4Pz9fU3jDhYMXKEG4sUW20DMpaaZY1opdyYGGfqJwSLdOqKXXCZtcPe9xEozVFkNtOE9AIB8Lq8YqstKCcRY+GVb+lqgNYbAPPUuy/6gPYuMo3nE0eTOm7I1RwmI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737762426; c=relaxed/simple; bh=fhv6fbic2s0quh3OAunJsF/luT1qeIOYufNBDSqGvto=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=ByZq489MJV7qn4TYnmnGx1YGOWB+QTiTVdAKJPJ40lvEedpjZqlXCB9Io+jz0IOPdJGchm8Lwo0vhErAjGkNZTP9elomZelaq7A69wDGhGOrOGTvHVPSI1ptbMisGRjyQPUQ5LPRmqxoObCmHE8zr7WGmaJeLK+WV68TShOejlc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Xe2xaP2z; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Xe2xaP2z" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2ef909597d9so7486352a91.3 for ; Fri, 24 Jan 2025 15:47:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1737762424; x=1738367224; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:reply-to:from:to:cc :subject:date:message-id:reply-to; bh=xZqSdmAP4JAfn0GgCRDW/fYFltIoNyRnJ22thKN56cQ=; b=Xe2xaP2z42NGdES5/jI+wFuLbu6PsGLHjyND7yNyq+Gw7UWQDBPUEzRm0+lpRKBZLB TssE1zjN/gYpos+APxLEB3JOT2qcHLZzo0KMeBqYLhmB8gTVReZDIzQtXFZiKf8xlvyA h+g6evoHjhReGrZUcxsgoIM5Zf1HTlSBxJdb837e9Ovv+LxIJ61Z55VGqz2UbOXrTAIV dIbk7UffljScaGU5Y+x7x7LFxmDaiYqaNe384PJ4DyMgeqHML0KpX7vVYnTOWpOKzngP 2ccDneq1ns8R3hUICg72C3SA7WoN/7bgfBWJns4oL2YRzqfg9O9on06aD0k44Z3JNkpT 8VuQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1737762424; x=1738367224; h=cc:to:from:subject:message-id:mime-version:date:reply-to :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=xZqSdmAP4JAfn0GgCRDW/fYFltIoNyRnJ22thKN56cQ=; b=FetMEN2Hv03xEUgoCZT2eNyIklUL2UwLaQG8lbVARzt/OqCKjv0uypFfW9JYZHuVdX DP1Kgdnm4dzibkq72KyWq7pElGSzB92fDH6nbY2Fnf8uCTU1zVVsfZJ/MSNj4D1rI5Yv DPEqfMa4vph9ldo+LiHFhhz3lfltxQy9NUbDOAr3yNKiFtiR1IFWE2Cr3OE8XPvbwPZO 0bixfuU9ABNbJDvyTYdtFOQ2i92gSLzj9LUW+USzZIRw5AqNyNfESiMxGDZxzCjga7Eh TO3TZViRjVjbZ/anPMi/7+YR8bg01wKx24WeYD7JXpyc+8o3QCI/g/MQRfw8iubWebMB 4suQ== X-Gm-Message-State: AOJu0Yyh/RQN/XL80fWpokAPYRHqqvNqses9IAGH43AkxrdKmsp8rdOS Tla8sUuUlZZT1nf8qfJNUfOLMgItf5C38aVZjsvfRCKZsOZGElWiwuFpv1QLCCqRA7MrMu8wozr jAw== X-Google-Smtp-Source: AGHT+IFiedBo0HwyMC9WduQOva9J3+TGiP5ylctgfBsgVX+RBYKVPFWUUH/l3n71CNB8yD1/yv+VcEwXHU8= X-Received: from pfbcz18.prod.google.com ([2002:aa7:9312:0:b0:72a:f9c7:a2ed]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:288e:b0:72d:2444:da2d with SMTP id d2e1a72fcca58-72dafa03216mr39235754b3a.9.1737762423719; Fri, 24 Jan 2025 15:47:03 -0800 (PST) Reply-To: Sean Christopherson Date: Fri, 24 Jan 2025 15:46:23 -0800 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.48.1.262.g85cc9f2d1e-goog Message-ID: <20250124234623.3609069-1-seanjc@google.com> Subject: [PATCH] KVM: x86/mmu: Ensure NX huge page recovery thread is alive before waking From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Keith Busch When waking a VM's NX huge page recovery thread, ensure the thread is actually alive before trying to wake it. Now that the thread is spawned on-demand during KVM_RUN, a VM without a recovery thread is reachable via the related module params. BUG: kernel NULL pointer dereference, address: 0000000000000040 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:vhost_task_wake+0x5/0x10 Call Trace: set_nx_huge_pages+0xcc/0x1e0 [kvm] param_attr_store+0x8a/0xd0 module_attr_store+0x1a/0x30 kernfs_fop_write_iter+0x12f/0x1e0 vfs_write+0x233/0x3e0 ksys_write+0x60/0xd0 do_syscall_64+0x5b/0x160 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f3b52710104 Modules linked in: kvm_intel kvm CR2: 0000000000000040 Fixes: 931656b9e2ff ("kvm: defer huge page recovery vhost task to later") Cc: stable@vger.kernel.org Cc: Keith Busch Signed-off-by: Sean Christopherson Reviewed-by: Keith Busch --- arch/x86/kvm/mmu/mmu.c | 33 ++++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) base-commit: f7bafceba76e9ab475b413578c1757ee18c3e44b diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index a45ae60e84ab..74c20dbb92da 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7120,6 +7120,19 @@ static void mmu_destroy_caches(void) kmem_cache_destroy(mmu_page_header_cache); } +static void kvm_wake_nx_recovery_thread(struct kvm *kvm) +{ + /* + * The NX recovery thread is spawned on-demand at the first KVM_RUN and + * may not be valid even though the VM is globally visible. Do nothing, + * as such a VM can't have any possible NX huge pages. + */ + struct vhost_task *nx_thread = READ_ONCE(kvm->arch.nx_huge_page_recovery_thread); + + if (nx_thread) + vhost_task_wake(nx_thread); +} + static int get_nx_huge_pages(char *buffer, const struct kernel_param *kp) { if (nx_hugepage_mitigation_hard_disabled) @@ -7180,7 +7193,7 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp) kvm_mmu_zap_all_fast(kvm); mutex_unlock(&kvm->slots_lock); - vhost_task_wake(kvm->arch.nx_huge_page_recovery_thread); + kvm_wake_nx_recovery_thread(kvm); } mutex_unlock(&kvm_lock); } @@ -7315,7 +7328,7 @@ static int set_nx_huge_pages_recovery_param(const char *val, const struct kernel mutex_lock(&kvm_lock); list_for_each_entry(kvm, &vm_list, vm_list) - vhost_task_wake(kvm->arch.nx_huge_page_recovery_thread); + kvm_wake_nx_recovery_thread(kvm); mutex_unlock(&kvm_lock); } @@ -7451,14 +7464,20 @@ static void kvm_mmu_start_lpage_recovery(struct once *once) { struct kvm_arch *ka = container_of(once, struct kvm_arch, nx_once); struct kvm *kvm = container_of(ka, struct kvm, arch); + struct vhost_task *nx_thread; kvm->arch.nx_huge_page_last = get_jiffies_64(); - kvm->arch.nx_huge_page_recovery_thread = vhost_task_create( - kvm_nx_huge_page_recovery_worker, kvm_nx_huge_page_recovery_worker_kill, - kvm, "kvm-nx-lpage-recovery"); + nx_thread = vhost_task_create(kvm_nx_huge_page_recovery_worker, + kvm_nx_huge_page_recovery_worker_kill, + kvm, "kvm-nx-lpage-recovery"); - if (kvm->arch.nx_huge_page_recovery_thread) - vhost_task_start(kvm->arch.nx_huge_page_recovery_thread); + if (!nx_thread) + return; + + vhost_task_start(nx_thread); + + /* Make the task visible only once it is fully started. */ + WRITE_ONCE(kvm->arch.nx_huge_page_recovery_thread, nx_thread); } int kvm_mmu_post_init_vm(struct kvm *kvm)