Re: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table

Avi Kivity
2011-06-29T09:17:00Z

On 06/22/2011 05:35 PM, Xiao Guangrong wrote:
> Use rcu to protect shadow pages table to be freed, so we can safely walk it,
> it should run fastly and is needed by mmio page fault
>

> static void kvm_mmu_commit_zap_page(struct kvm *kvm,
> struct list_head *invalid_list)
> {
> @@ -1767,6 +1874,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>
> kvm_flush_remote_tlbs(kvm);
>
> + if (atomic_read(&kvm->arch.reader_counter)) {
> + kvm_mmu_isolate_pages(invalid_list);
> + sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
> + list_del_init(invalid_list);
> + call_rcu(&sp->rcu, free_pages_rcu);
> + return;
> + }
> +

I think we should do this unconditionally. The cost of ping-ponging the
shared cache line containing reader_counter will increase with large smp
counts. On the other hand, zap_page is very rare, so it can be a little
slower. Also, less code paths = easier to understand.

--
error compiling committee.c: too many arguments to function