Messages in this thread | | | Date | Thu, 3 Nov 2022 16:23:12 +0100 | Subject | Re: [PATCH 39/44] KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock | From | Paolo Bonzini <> |
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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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