Re: KVM: x86: use dynamic percpu allocations for shared msrs area

[Gleb Natapov <gleb@redhat.com>]

On Thu, Jan 03, 2013 at 11:41:39AM -0200, Marcelo Tosatti wrote:
> 
> Andy, Mike, can you confirm whether this fixes the percpu allocation
> failures when loading kvm.ko? TIA
> 
> ----
> 
> Use dynamic percpu allocations for the shared msrs structure, 
> to avoid using the limited reserved percpu space.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
Reviewed-by: Gleb Natapov <gleb@redhat.com>

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1c9c834..5229a67 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -120,7 +120,7 @@ struct kvm_shared_msrs {
>  };
>  
>  static struct kvm_shared_msrs_global __read_mostly shared_msrs_global;
> -static DEFINE_PER_CPU(struct kvm_shared_msrs, shared_msrs);
> +static struct kvm_shared_msrs __percpu *shared_msrs;
>  
>  struct kvm_stats_debugfs_item debugfs_entries[] = {
>  	{ "pf_fixed", VCPU_STAT(pf_fixed) },
> @@ -191,10 +191,10 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
>  
>  static void shared_msr_update(unsigned slot, u32 msr)
>  {
> -	struct kvm_shared_msrs *smsr;
>  	u64 value;
> +	unsigned int cpu = smp_processor_id();
> +	struct kvm_shared_msrs *smsr = per_cpu_ptr(shared_msrs, cpu);
>  
> -	smsr = &__get_cpu_var(shared_msrs);
>  	/* only read, and nobody should modify it at this time,
>  	 * so don't need lock */
>  	if (slot >= shared_msrs_global.nr) {
> @@ -226,7 +226,8 @@ static void kvm_shared_msr_cpu_online(void)
>  
>  void kvm_set_shared_msr(unsigned slot, u64 value, u64 mask)
>  {
> -	struct kvm_shared_msrs *smsr = &__get_cpu_var(shared_msrs);
> +	unsigned int cpu = smp_processor_id();
> +	struct kvm_shared_msrs *smsr = per_cpu_ptr(shared_msrs, cpu);
>  
>  	if (((value ^ smsr->values[slot].curr) & mask) == 0)
>  		return;
> @@ -242,7 +243,8 @@ EXPORT_SYMBOL_GPL(kvm_set_shared_msr);
>  
>  static void drop_user_return_notifiers(void *ignore)
>  {
> -	struct kvm_shared_msrs *smsr = &__get_cpu_var(shared_msrs);
> +	unsigned int cpu = smp_processor_id();
> +	struct kvm_shared_msrs *smsr = per_cpu_ptr(shared_msrs, cpu);
>  
>  	if (smsr->registered)
>  		kvm_on_user_return(&smsr->urn);
> @@ -5233,9 +5235,16 @@ int kvm_arch_init(void *opaque)
>  		goto out;
>  	}
>  
> +	r = -ENOMEM;
> +	shared_msrs = alloc_percpu(struct kvm_shared_msrs);
> +	if (!shared_msrs) {
> +		printk(KERN_ERR "kvm: failed to allocate percpu kvm_shared_msrs\n");
> +		goto out;
> +	}
> +
>  	r = kvm_mmu_module_init();
>  	if (r)
> -		goto out;
> +		goto out_free_percpu;
>  
>  	kvm_set_mmio_spte_mask();
>  	kvm_init_msr_list();
> @@ -5258,6 +5267,8 @@ int kvm_arch_init(void *opaque)
>  
>  	return 0;
>  
> +out_free_percpu:
> +	free_percpu(shared_msrs);
>  out:
>  	return r;
>  }
> @@ -5275,6 +5286,7 @@ void kvm_arch_exit(void)
>  #endif
>  	kvm_x86_ops = NULL;
>  	kvm_mmu_module_exit();
> +	free_percpu(shared_msrs);
>  }
>  
>  int kvm_emulate_halt(struct kvm_vcpu *vcpu)
> --
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--
			Gleb.