Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path

Avi Kivity
2010-04-12T10:25:58Z

On 04/12/2010 12:22 PM, Xiao Guangrong wrote:
> Hi Avi,
>
> Avi Kivity wrote:
>
>
>> hlist_for_each_entry_safe() is supposed to be be safe against removal of
>> the element that is pointed to by the iteration cursor.
>>
> If we destroyed the next point, hlist_for_each_entry_safe() is unsafe.
>
> List hlist_for_each_entry_safe()'s code:
>
> |#define hlist_for_each_entry_safe(tpos, pos, n, head, member) \
> | for (pos = (head)->first; \
> | pos&& ({ n = pos->next; 1; })&& \
> | ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
> | pos = n)
>
> if n is destroyed:
> 'pos = n, n = pos->next'
> then it access n again, it's unsafe/illegal for us.
>

But kvm_mmu_zap_page() will only destroy sp == tpos == pos; n points at
pos->next already, so it's safe.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.