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([2001:b07:6468:f312:59c7:c3ee:2dec:d2b4]) by smtp.gmail.com with ESMTPSA id 16sm6300278wmi.0.2020.02.14.00.58.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Feb 2020 00:58:38 -0800 (PST) Subject: Re: [PATCH RESEND] KVM: X86: Grab KVM's srcu lock when accessing hv assist page To: Wanpeng Li , LKML , kvm Cc: Sean Christopherson , Wanpeng Li , Vitaly Kuznetsov , Jim Mattson , Joerg Roedel References: From: Paolo Bonzini Message-ID: <353a53a7-5d1e-1797-c870-1eb8b382bedd@redhat.com> Date: Fri, 14 Feb 2020 09:58:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/02/20 09:51, Wanpeng Li wrote: > From: Wanpeng Li > > Acquire kvm->srcu for the duration of mapping eVMCS to fix a bug where accessing > hv assist page derefences ->memslots without holding ->srcu or ->slots_lock. Perhaps nested_sync_vmcs12_to_shadow should be moved to prepare_guest_switch, where the SRCU is already taken. 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/nested.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > index 657c2ed..a68a69d 100644 > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -1994,14 +1994,18 @@ static int > nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu, > void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu) > { > struct vcpu_vmx *vmx = to_vmx(vcpu); > + int idx; > > /* > * hv_evmcs may end up being not mapped after migration (when > * L2 was running), map it here to make sure vmcs12 changes are > * properly reflected. > */ > - if (vmx->nested.enlightened_vmcs_enabled && !vmx->nested.hv_evmcs) > + if (vmx->nested.enlightened_vmcs_enabled && !vmx->nested.hv_evmcs) { > + idx = srcu_read_lock(&vcpu->kvm->srcu); > nested_vmx_handle_enlightened_vmptrld(vcpu, false); > + srcu_read_unlock(&vcpu->kvm->srcu, idx); > + } > > if (vmx->nested.hv_evmcs) { > copy_vmcs12_to_enlightened(vmx); > -- > 2.7.4 >