On 11/3/22 00:19, Sean Christopherson wrote:
+- kvm_lock is taken outside kvm->mmu_lock
Not surprising since one is a mutex and one is an rwlock. :) You can
drop this hunk as well as the "Opportunistically update KVM's locking
documentation" sentence in the commit message.
- vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock
- kvm->arch.mmu_lock is an rwlock. kvm->arch.tdp_mmu_pages_lock and
@@ -216,15 +220,11 @@ time it will be set using the Dirty tracking mechanism
described above.
:Type: mutex
:Arch: any
:Protects: - vm_list
-
-``kvm_count_lock``
-^^^^^^^^^^^^^^^^^^
-
-:Type: raw_spinlock_t
-:Arch: any
-:Protects: - hardware virtualization enable/disable
-:Comment: 'raw' because hardware enabling/disabling must be atomic /wrt
- migration.
+ - kvm_usage_count
+ - hardware virtualization enable/disable
+ - module probing (x86 only)
What do you mean exactly by "module probing"? Is it anything else than
what is serialized by vendor_module_lock?
Paolo
+:Comment: KVM also disables CPU hotplug via cpus_read_lock() during
+ enable/disable.
``kvm->mn_invalidate_lock``
^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4e765ef9f4bd..c8d92e6c3922 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -100,7 +100,6 @@ EXPORT_SYMBOL_GPL(halt_poll_ns_shrink);
*/
DEFINE_MUTEX(kvm_lock);
-static DEFINE_RAW_SPINLOCK(kvm_count_lock);
LIST_HEAD(vm_list);
static cpumask_var_t cpus_hardware_enabled;
@@ -5028,9 +5027,10 @@ static void hardware_enable_nolock(void *junk)
static int kvm_online_cpu(unsigned int cpu)
{
+ unsigned long flags;
int ret = 0;
- raw_spin_lock(&kvm_count_lock);
+ mutex_lock(&kvm_lock);
/*
* Abort the CPU online process if hardware virtualization cannot
* be enabled. Otherwise running VMs would encounter unrecoverable
@@ -5039,13 +5039,16 @@ static int kvm_online_cpu(unsigned int cpu)
if (kvm_usage_count) {
WARN_ON_ONCE(atomic_read(&hardware_enable_failed));
+ local_irq_save(flags);
hardware_enable_nolock(NULL);
+ local_irq_restore(flags);
+
if (atomic_read(&hardware_enable_failed)) {
atomic_set(&hardware_enable_failed, 0);
ret = -EIO;
}
}
- raw_spin_unlock(&kvm_count_lock);
+ mutex_unlock(&kvm_lock);
return ret;
}
@@ -5061,10 +5064,13 @@ static void hardware_disable_nolock(void *junk)
static int kvm_offline_cpu(unsigned int cpu)
{
- raw_spin_lock(&kvm_count_lock);
- if (kvm_usage_count)
+ mutex_lock(&kvm_lock);
+ if (kvm_usage_count) {
+ preempt_disable();
hardware_disable_nolock(NULL);
- raw_spin_unlock(&kvm_count_lock);
+ preempt_enable();
+ }
+ mutex_unlock(&kvm_lock);
return 0;
}
@@ -5079,9 +5085,11 @@ static void hardware_disable_all_nolock(void)
static void hardware_disable_all(void)
{
- raw_spin_lock(&kvm_count_lock);
+ cpus_read_lock();
+ mutex_lock(&kvm_lock);
hardware_disable_all_nolock();
- raw_spin_unlock(&kvm_count_lock);
+ mutex_unlock(&kvm_lock);
+ cpus_read_unlock();
}
static int hardware_enable_all(void)
@@ -5097,7 +5105,7 @@ static int hardware_enable_all(void)
* Disable CPU hotplug to prevent scenarios where KVM sees
*/
cpus_read_lock();
- raw_spin_lock(&kvm_count_lock);
+ mutex_lock(&kvm_lock);
kvm_usage_count++;
if (kvm_usage_count == 1) {
@@ -5110,7 +5118,7 @@ static int hardware_enable_all(void)
}
}
- raw_spin_unlock(&kvm_count_lock);
+ mutex_unlock(&kvm_lock);
cpus_read_unlock();
return r;
@@ -5716,6 +5724,15 @@ static void kvm_init_debug(void)
static int kvm_suspend(void)
{
+ /*
+ * Secondary CPUs and CPU hotplug are disabled across the suspend/resume
+ * callbacks, i.e. no need to acquire kvm_lock to ensure the usage count
+ * is stable. Assert that kvm_lock is not held as a paranoid sanity
+ * check that the system isn't suspended when KVM is enabling hardware.
+ */
+ lockdep_assert_not_held(&kvm_lock);
+ lockdep_assert_irqs_disabled();
+
if (kvm_usage_count)
hardware_disable_nolock(NULL);
return 0;
@@ -5723,10 +5740,11 @@ static int kvm_suspend(void)
static void kvm_resume(void)
{
- if (kvm_usage_count) {
- lockdep_assert_not_held(&kvm_count_lock);
+ lockdep_assert_not_held(&kvm_lock);
+ lockdep_assert_irqs_disabled();
+
+ if (kvm_usage_count)
hardware_enable_nolock(NULL);
- }
}
static struct syscore_ops kvm_syscore_ops = {
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