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Wed, 02 Nov 2022 16:20:19 -0700 (PDT) Date: Wed, 2 Nov 2022 23:19:05 +0000 In-Reply-To: <20221102231911.3107438-1-seanjc@google.com> Mime-Version: 1.0 References: <20221102231911.3107438-1-seanjc@google.com> X-Mailer: git-send-email 2.38.1.431.g37b22c650d-goog Message-ID: <20221102231911.3107438-39-seanjc@google.com> Subject: [PATCH 38/44] KVM: Disable CPU hotplug during hardware enabling From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Huacai Chen , Aleksandar Markovic , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Matthew Rosato , Eric Farman , Sean Christopherson , Vitaly Kuznetsov Content-Type: text/plain; charset="UTF-8" X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Cc: kvm@vger.kernel.org, David Hildenbrand , Atish Patra , linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-s390@vger.kernel.org, Chao Gao , Suzuki K Poulose , Yuan Yao , kvmarm@lists.linux.dev, Thomas Gleixner , Alexandru Elisei , linux-arm-kernel@lists.infradead.org, Isaku Yamahata , Fabiano Rosas , linux-mips@vger.kernel.org, Oliver Upton , James Morse , kvm-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Chao Gao Disable CPU hotplug during hardware_enable_all() to prevent the corner case where if the following sequence occurs: 1. A hotplugged CPU marks itself online in cpu_online_mask 2. The hotplugged CPU enables interrupt before invoking KVM's ONLINE callback 3 hardware_enable_all() is invoked on another CPU right the hotplugged CPU will be included in on_each_cpu() and thus get sent through hardware_enable_nolock() before kvm_online_cpu() is called. start_secondary { ... set_cpu_online(smp_processor_id(), true); <- 1 ... local_irq_enable(); <- 2 ... cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); <- 3 } KVM currently fudges around this race by keeping track of which CPUs have done hardware enabling (see commit 1b6c016818a5 "KVM: Keep track of which cpus have virtualization enabled"), but that's an inefficient, convoluted, and hacky solution. Signed-off-by: Chao Gao [sean: split to separate patch, write changelog] Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 8 +++++++- virt/kvm/kvm_main.c | 10 ++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a7b1d916ecb2..a15e54ba0471 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9283,7 +9283,13 @@ static int kvm_x86_check_processor_compatibility(struct kvm_x86_init_ops *ops) int cpu = smp_processor_id(); struct cpuinfo_x86 *c = &cpu_data(cpu); - WARN_ON(!irqs_disabled()); + /* + * Compatibility checks are done when loading KVM and when enabling + * hardware, e.g. during CPU hotplug, to ensure all online CPUs are + * compatible, i.e. KVM should never perform a compatibility check on + * an offline CPU. + */ + WARN_ON(!irqs_disabled() && cpu_active(cpu)); if (__cr4_reserved_bits(cpu_has, c) != __cr4_reserved_bits(cpu_has, &boot_cpu_data)) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index fd9e39c85549..4e765ef9f4bd 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -5088,6 +5088,15 @@ static int hardware_enable_all(void) { int r = 0; + /* + * When onlining a CPU, cpu_online_mask is set before kvm_online_cpu() + * is called, and so on_each_cpu() between them includes the CPU that + * is being onlined. As a result, hardware_enable_nolock() may get + * invoked before kvm_online_cpu(). + * + * Disable CPU hotplug to prevent scenarios where KVM sees + */ + cpus_read_lock(); raw_spin_lock(&kvm_count_lock); kvm_usage_count++; @@ -5102,6 +5111,7 @@ static int hardware_enable_all(void) } raw_spin_unlock(&kvm_count_lock); + cpus_read_unlock(); return r; } -- 2.38.1.431.g37b22c650d-goog