From mboxrd@z Thu Jan 1 00:00:00 1970 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 C9E68C433EF for ; Thu, 10 Mar 2022 03:35:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239302AbiCJDge (ORCPT ); Wed, 9 Mar 2022 22:36:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52140 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235161AbiCJDgc (ORCPT ); Wed, 9 Mar 2022 22:36:32 -0500 Received: from zg8tmty1ljiyny4xntqumjca.icoremail.net (zg8tmty1ljiyny4xntqumjca.icoremail.net [165.227.154.27]) by lindbergh.monkeyblade.net (Postfix) with SMTP id 5CF505EBD8; Wed, 9 Mar 2022 19:35:27 -0800 (PST) Received: from [172.19.1.222] (unknown [59.61.78.132]) by app2 (Coremail) with SMTP id 4zNnewBXXs65cSliXZEBAA--.158S3; Thu, 10 Mar 2022 11:34:20 +0800 (CST) Message-ID: <69d9a292-c140-ac6c-6afb-df4e383e2847@wangsu.com> Date: Thu, 10 Mar 2022 11:34:16 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 From: Xinlong Lin Subject: Re: [RESEND PATCH] KVM: x86/mmu: make apf token non-zero to fix bug To: Liang Zhang , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org Cc: pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, wangzhigang17@huawei.com References: <20220222031239.1076682-1-zhangliang5@huawei.com> In-Reply-To: <20220222031239.1076682-1-zhangliang5@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID: 4zNnewBXXs65cSliXZEBAA--.158S3 X-Coremail-Antispam: 1UD129KBjvJXoWxZw1ruw18Jr18XFyUJF15XFb_yoW5ArW7pF y2kryFgw4rXr1Yg3WUXwn0vr45Cr48CF1xXr9rGrW8Z3WYqw1kCF1xKrZ8ZF93Wr48Za1f tFsYqw4Ykr18JaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkSb7Iv0xC_Cr1lb4IE77IF4wAFc2x0x2IEx4CE42xK8VAvwI8I cIk0rVWrJVCq3wA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK021l84ACjcxK6xIIjx v20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26F4UJVW0owA2z4x0Y4vE x4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oVCq3wAS0I0E0xvYzx vE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VCjz48v1sIEY20_Gr4l Ox8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7Mx k0xIA0c2IEe2xFo4CEbIxvr21lc2xSY4AK67AK6r48MxAIw28IcxkI7VAKI48JMxAIw28I cVCjz48v1sIEY20_Gr4l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJV WUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIYrxkI7VAK I48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r4j6F 4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY 6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxU8jg4DUUUU X-CM-SenderInfo: holq5zmt6zt0xjvxhudrp/ Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/2/22 11:12, Liang Zhang wrote: > In current async pagefault logic, when a page is ready, KVM relies on > kvm_arch_can_dequeue_async_page_present() to determine whether to deliver > a READY event to the Guest. This function test token value of struct > kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a > READY event is finished by Guest. If value is zero meaning that a READY > event is done, so the KVM can deliver another. > But the kvm_arch_setup_async_pf() may produce a valid token with zero > value, which is confused with previous mention and may lead the loss of > this READY event. > > This bug may cause task blocked forever in Guest: > INFO: task stress:7532 blocked for more than 1254 seconds. > Not tainted 5.10.0 #16 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:stress state:D stack: 0 pid: 7532 ppid: 1409 > flags:0x00000080 > Call Trace: > __schedule+0x1e7/0x650 > schedule+0x46/0xb0 > kvm_async_pf_task_wait_schedule+0xad/0xe0 > ? exit_to_user_mode_prepare+0x60/0x70 > __kvm_handle_async_pf+0x4f/0xb0 > ? asm_exc_page_fault+0x8/0x30 > exc_page_fault+0x6f/0x110 > ? asm_exc_page_fault+0x8/0x30 > asm_exc_page_fault+0x1e/0x30 > RIP: 0033:0x402d00 > RSP: 002b:00007ffd31912500 EFLAGS: 00010206 > RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0 > RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0 > RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086 > R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000 > R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000 > > Signed-off-by: Liang Zhang > --- > arch/x86/kvm/mmu/mmu.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 593093b52395..8e24f73bf60b 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3889,12 +3889,23 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr) > walk_shadow_page_lockless_end(vcpu); > } > > +static u32 alloc_apf_token(struct kvm_vcpu *vcpu) > +{ > + /* make sure the token value is not 0 */ > + u32 id = vcpu->arch.apf.id; > + > + if (id << 12 == 0) > + vcpu->arch.apf.id = 1; > + > + return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; > +} > + > static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > gfn_t gfn) > { > struct kvm_arch_async_pf arch; > > - arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; This patch is completely OK. But I have a question, can we simplify it to arch.token = (++vcpu->arch.apf.id << 12) | vcpu->vcpu_id; > + arch.token = alloc_apf_token(vcpu); > arch.gfn = gfn; > arch.direct_map = vcpu->arch.mmu->direct_map; > arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu);