From e4aa7f88af1a123863530af4a238ce64ec8fad5a Mon Sep 17 00:00:00 2001 From: Chao Gao Date: Wed, 30 Nov 2022 23:09:26 +0000 Subject: KVM: Disable CPU hotplug during hardware enabling/disabling Disable CPU hotplug when enabling/disabling hardware 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_{en,dis}able_all() is invoked on another CPU the hotplugged CPU will be included in on_each_cpu() and thus get sent through hardware_{en,dis}able_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 Message-Id: <20221130230934.1014142-43-seanjc@google.com> Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'virt') diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index ee1005cb99e17..2d6203ecab883 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -5167,15 +5167,26 @@ static void hardware_disable_all_nolock(void) static void hardware_disable_all(void) { + cpus_read_lock(); raw_spin_lock(&kvm_count_lock); hardware_disable_all_nolock(); raw_spin_unlock(&kvm_count_lock); + cpus_read_unlock(); } 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(), which also enables hardware if the + * usage count is non-zero. Disable CPU hotplug to avoid attempting to + * enable hardware multiple times. + */ + cpus_read_lock(); raw_spin_lock(&kvm_count_lock); kvm_usage_count++; @@ -5190,6 +5201,7 @@ static int hardware_enable_all(void) } raw_spin_unlock(&kvm_count_lock); + cpus_read_unlock(); return r; } -- cgit 1.2.3-korg