Re: [PATCH 09/15] KVM: MMU: split kvm_mmu_free_page

Xiao Guangrong
2011-06-13T03:13:22Z

On 06/12/2011 04:33 PM, Avi Kivity wrote:
> On 06/10/2011 06:50 AM, Xiao Guangrong wrote:
>> >> +static void kvm_mmu_free_unlock_parts(struct kvm_mmu_page *sp)
>> >> +{
>> >> + list_del(&sp->link);
>> >> + free_page((unsigned long)sp->spt);
>> >> kmem_cache_free(mmu_page_header_cache, sp);
>> >> }
>> >
>> > The list_del() must be run under a lock, no? it can access kvm->arch.active_mmu_pages.
>> >
>>
>> In prepare path, we have moved the sp from active_mmu_pages to invlaid_list.
>
> It still needs to be accessed under a lock, no matter which list is used.
>

Actually, if we need to free page in RCU context, we unlink them from invalid_list firstly:

if (atomic_read(&kvm->arch.reader_counter)) {
......
list_del_init(invalid_list);
trace_kvm_mmu_delay_free_pages(sp);
call_rcu(&sp->rcu, free_invalid_pages_rcu);
return;
}

Then, global list is not used anymore.