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authorChao Gao <chao.gao@intel.com>2022-12-01 02:09:26 +0300
committerPaolo Bonzini <pbonzini@redhat.com>2022-12-29 23:48:32 +0300
commite4aa7f88af1a123863530af4a238ce64ec8fad5a (patch)
tree5c167c438350d01898a772cd24d49736b2dda32b /virt
parentaaf12a7b4323eb7d94677bcefc286ff6b772ed1c (diff)
downloadlinux-e4aa7f88af1a123863530af4a238ce64ec8fad5a.tar.xz
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 <chao.gao@intel.com> [sean: split to separate patch, write changelog] Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20221130230934.1014142-43-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/kvm_main.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ee1005cb99e1..2d6203ecab88 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;
}