Re: [PATCH 02/13] KVM: MMU: abstract spte write-protect

Xiao Guangrong
2012-03-29T11:51:38Z

On 03/29/2012 07:11 PM, Avi Kivity wrote:

>> +/* Return true if the spte is dropped. */
>> +static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool large,
>> + int *flush)
>
> bool *flush
>

Okay, will fix.

>> +{
>> + u64 spte = *sptep;
>> +
>> + if (!is_writable_pte(spte))
>> + return false;
>> +
>> + *flush |= true;
>> +
>> + if (large) {
>> + pgprintk("rmap_write_protect(large): spte %p %llx\n",
>> + spte, *spte);
>> + BUG_ON(!is_large_pte(spte));
>> +
>> + drop_spte(kvm, sptep);
>> + --kvm->stat.lpages;
>> + return true;
>> + }
>
> As I mentioned before, write-protecting a large spte is a good idea,
> since it moves some work from protect-time to fault-time, so it reduces
> jitter. This removes the need for the return value.
>
> It may also be a good idea to populate the lower level instead of
> dropping the spte.
>
> All outside this patch set of course. I'd add those ideas to the wiki
> but it won't let me edit at the moment.
>

I saw your idea, i will pick it up after this patch if no one does it
at that time. :)