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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 7796DC3B1BF for ; Fri, 14 Feb 2020 21:34:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 50CFC222C4 for ; Fri, 14 Feb 2020 21:34:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388686AbgBNVd6 (ORCPT ); Fri, 14 Feb 2020 16:33:58 -0500 Received: from mga14.intel.com ([192.55.52.115]:65043 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388332AbgBNVd6 (ORCPT ); Fri, 14 Feb 2020 16:33:58 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Feb 2020 13:33:57 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,441,1574150400"; d="scan'208";a="223151442" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga007.jf.intel.com with ESMTP; 14 Feb 2020 13:33:57 -0800 Date: Fri, 14 Feb 2020 13:33:57 -0800 From: Sean Christopherson To: Paolo Bonzini Cc: Wanpeng Li , LKML , kvm , Wanpeng Li , Vitaly Kuznetsov , Jim Mattson , Joerg Roedel Subject: Re: [PATCH v2] KVM: X86: Grab KVM's srcu lock when accessing hv assist page Message-ID: <20200214213357.GH20690@linux.intel.com> References: <7171e537-27f9-c1e5-ae32-9305710be2c7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7171e537-27f9-c1e5-ae32-9305710be2c7@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org The subject shoud be rewritten to simply states that the vmcs12->shadow sync is being. The changelog can explain the motiviation, but a one-line git log should clearly reveal that this affects the shadow VMCS. Subsystem should also be "KVM: nVMX:" On Fri, Feb 14, 2020 at 10:27:12AM +0100, Paolo Bonzini wrote: > On 14/02/20 10:16, Wanpeng Li wrote: > > From: wanpeng li > > > > For the duration of mapping eVMCS, it derefences ->memslots without holding > > ->srcu or ->slots_lock when accessing hv assist page. This patch fixes it by > > moving nested_sync_vmcs12_to_shadow to prepare_guest_switch, where the SRCU > > is already taken. > > Looks good, but I'd like an extra review from Sean or Vitaly. > > We also should add a WARN_ON_ONCE that replaces the previous location of > the "if (vmx->nested.need_vmcs12_to_shadow_sync)", but I can do that myself. > > Thanks, > > Paolo > > > It can be reproduced by running kvm's evmcs_test selftest. > > > > ============================= > > warning: suspicious rcu usage > > 5.6.0-rc1+ #53 tainted: g w ioe > > ----------------------------- > > ./include/linux/kvm_host.h:623 suspicious rcu_dereference_check() usage! > > > > other info that might help us debug this: > > > > rcu_scheduler_active = 2, debug_locks = 1 > > 1 lock held by evmcs_test/8507: > > #0: ffff9ddd156d00d0 (&vcpu->mutex){+.+.}, at: > > kvm_vcpu_ioctl+0x85/0x680 [kvm] > > > > stack backtrace: > > cpu: 6 pid: 8507 comm: evmcs_test tainted: g w ioe 5.6.0-rc1+ #53 > > hardware name: dell inc. optiplex 7040/0jctf8, bios 1.4.9 09/12/2016 > > call trace: > > dump_stack+0x68/0x9b > > kvm_read_guest_cached+0x11d/0x150 [kvm] > > kvm_hv_get_assist_page+0x33/0x40 [kvm] > > nested_enlightened_vmentry+0x2c/0x60 [kvm_intel] > > nested_vmx_handle_enlightened_vmptrld.part.52+0x32/0x1c0 [kvm_intel] > > nested_sync_vmcs12_to_shadow+0x439/0x680 [kvm_intel] > > vmx_vcpu_run+0x67a/0xe60 [kvm_intel] > > vcpu_enter_guest+0x35e/0x1bc0 [kvm] > > kvm_arch_vcpu_ioctl_run+0x40b/0x670 [kvm] > > kvm_vcpu_ioctl+0x370/0x680 [kvm] > > ksys_ioctl+0x235/0x850 > > __x64_sys_ioctl+0x16/0x20 > > do_syscall_64+0x77/0x780 > > entry_syscall_64_after_hwframe+0x49/0xbe > > > > Signed-off-by: Wanpeng Li > > --- > > arch/x86/kvm/vmx/vmx.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index 9a66648..6bd6ca4 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -1214,6 +1214,9 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > > > > vmx_set_host_fs_gs(host_state, fs_sel, gs_sel, fs_base, gs_base); > > vmx->guest_state_loaded = true; > > + > > + if (vmx->nested.need_vmcs12_to_shadow_sync) > > + nested_sync_vmcs12_to_shadow(vcpu); This needs to be above the short circuit check on guest_state_loaded, e.g.: if (vmx->nested.need_vmcs12_to_shadow_sync) nested_sync_vmcs12_to_shadow(vcpu); if (vmx->guest_state_loaded) return; > > } > > > > static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx) > > @@ -6480,9 +6483,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) > > vmcs_write32(PLE_WINDOW, vmx->ple_window); > > } > > > > - if (vmx->nested.need_vmcs12_to_shadow_sync) > > - nested_sync_vmcs12_to_shadow(vcpu); > > - > > if (kvm_register_is_dirty(vcpu, VCPU_REGS_RSP)) > > vmcs_writel(GUEST_RSP, vcpu->arch.regs[VCPU_REGS_RSP]); > > if (kvm_register_is_dirty(vcpu, VCPU_REGS_RIP)) > > -- > > 2.7.4 > > >