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[54.240.197.233]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38bf3221c25sm13552937f8f.23.2025.01.21.08.01.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2025 08:01:36 -0800 (PST) From: Paul Durrant X-Google-Original-From: Paul Durrant Message-ID: <5cc5a8ef-b405-44f8-b799-ec9db39ac695@xen.org> Date: Tue, 21 Jan 2025 16:01:33 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: paul@xen.org Subject: Re: [PATCH 01/10] KVM: x86: Don't take kvm->lock when iterating over vCPUs in suspend notifier To: Sean Christopherson , Paolo Bonzini , David Woodhouse Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+352e553a86e0d75f5120@syzkaller.appspotmail.com, Paul Durrant , David Woodhouse , Vitaly Kuznetsov References: <20250118005552.2626804-1-seanjc@google.com> <20250118005552.2626804-2-seanjc@google.com> Content-Language: en-US Organization: Xen Project In-Reply-To: <20250118005552.2626804-2-seanjc@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18/01/2025 00:55, Sean Christopherson wrote: > When queueing vCPU PVCLOCK updates in response to SUSPEND or HIBERNATE, > don't take kvm->lock as doing so can trigger a largely theoretical > deadlock, it is perfectly safe to iterate over the xarray of vCPUs without > holding kvm->lock, and kvm->lock doesn't protect kvm_set_guest_paused() in > any way (pv_time.active and pvclock_set_guest_stopped_request are > protected by vcpu->mutex, not kvm->lock). > > Reported-by: syzbot+352e553a86e0d75f5120@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/677c0f36.050a0220.3b3668.0014.GAE@google.com > Fixes: 7d62874f69d7 ("kvm: x86: implement KVM PM-notifier") > Signed-off-by: Sean Christopherson Reviewed-by: Paul Durrant