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Thu, 28 Aug 2025 09:44:30 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFOQ697WbVXyU99n0waspLzqYpTQQBImj5MyrGfz7lwIURmhpghnGB5Sbe7cWt+MuicJOIRjj3b26keLzpmBNo= X-Received: by 2002:a05:600c:4715:b0:456:302:6dc3 with SMTP id 5b1f17b1804b1-45b517d4c47mr197983995e9.26.1756399470139; Thu, 28 Aug 2025 09:44:30 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250827152754.12481-1-lifei.shirley@bytedance.com> In-Reply-To: From: Paolo Bonzini Date: Thu, 28 Aug 2025 18:44:18 +0200 X-Gm-Features: Ac12FXxy8RFR1sySn2cIpHgzn1YV9jdcFkuTVaa1o9x9iu2acXvfPgiJQStuG6A Message-ID: Subject: Re: [External] Re: [PATCH] KVM: x86: Latch INITs only in specific CPU states in KVM_SET_VCPU_EVENTS To: Fei Li Cc: Sean Christopherson , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, liran.alon@oracle.com, hpa@zytor.com, wanpeng.li@hotmail.com, kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Aug 28, 2025 at 5:13=E2=80=AFPM Fei Li wrote: > Actually this is a bug triggered by one monitor tool in our production > environment. This monitor executes 'info registers -a' hmp at a fixed > frequency, even during VM startup process, which makes some AP stay in > KVM_MP_STATE_UNINITIALIZED forever. But this race only occurs with > extremely low probability, about 1~2 VM hangs per week. > > Considering other emulators, like cloud-hypervisor and firecracker maybe > also have similar potential race issues, I think KVM had better do some > handling. But anyway, I will check Qemu code to avoid such race. Thanks > for both of your comments. =F0=9F=99=82 If you can check whether other emulators invoke KVM_SET_VCPU_EVENTS in similar cases, that of course would help understanding the situation better. In QEMU, it is possible to delay KVM_GET_VCPU_EVENTS until after all vCPUs have halted. Paolo