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 5870FC433F5 for ; Thu, 10 Mar 2022 03:42:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239252AbiCJDnn (ORCPT ); Wed, 9 Mar 2022 22:43:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36516 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231249AbiCJDnl (ORCPT ); Wed, 9 Mar 2022 22:43:41 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69485CC50D; Wed, 9 Mar 2022 19:42:40 -0800 (PST) Received: from dggpemm500022.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KDZYD3SlWz9sVT; Thu, 10 Mar 2022 11:38:56 +0800 (CST) Received: from dggpemm500003.china.huawei.com (7.185.36.56) by dggpemm500022.china.huawei.com (7.185.36.162) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Thu, 10 Mar 2022 11:42:38 +0800 Received: from [10.174.185.129] (10.174.185.129) by dggpemm500003.china.huawei.com (7.185.36.56) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Thu, 10 Mar 2022 11:42:37 +0800 Message-ID: Date: Thu, 10 Mar 2022 11:42:37 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [RESEND PATCH] KVM: x86/mmu: make apf token non-zero to fix bug Content-Language: en-US To: Xinlong Lin , , , , , CC: , , , , , , , , References: <20220222031239.1076682-1-zhangliang5@huawei.com> <69d9a292-c140-ac6c-6afb-df4e383e2847@wangsu.com> From: "zhangliang (AG)" In-Reply-To: <69d9a292-c140-ac6c-6afb-df4e383e2847@wangsu.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.185.129] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500003.china.huawei.com (7.185.36.56) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org No. Because '(++vcpu->arch.apf.id << 12)' may also produce zero value. On 2022/3/10 11:34, Xinlong Lin wrote: > > > 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); > > . -- Best Regards, Liang Zhang