On 24/06/19 11:09, Peter Xu wrote:
> On Mon, Jun 24, 2019 at 10:43:21AM +0200, Paolo Bonzini wrote:
>> On 24/06/19 10:06, Peter Xu wrote:
>>> Well, if with such an error we'd better fix it right away in this
>>> patch... :)
>>>
>>> Let me wait for some more comments, I'll touch that up too if I need a
>>> repost.
>>
>> Looks good to me, except for one minor issue in this patch. But do not
>> attribute this one to me, it's basically all code from you.
>
> OK.
>
>>
>>> +static uint64_t vtd_get_next_mask(uint64_t start, uint64_t size, int gaw)
>>> +{
>>> + /* Tries to find smallest mask from start first */
>>> + uint64_t rmask = start & -start, max_mask = 1ULL << gaw;
>>> +
>>> + assert(size && gaw > 0 && gaw < 64);
>>> +
>>> + /* Zero start, or too big */
>>> + if (!rmask || rmask > max_mask) {
>>> + rmask = max_mask;
>>> + }
>>
>> Perhaps simpler:
>>
>> uint64_t max_mask = 1ULL << gaw;
>> uint64_t alignment = start ? start & -start : max_mask;
>>
>
> (I'll add another "alignment = MIN(alignment, max_mask)" here if no
> one disagree...)
I do! :) If alignment > max_mask, then it will also be > size below so
clamping is unnecessary.
There is another way which is to compute on the mask, so that start == 0
underflows to all-ones:
uint64_t max_mask = (1ULL << gaw) - 1;
uint64_t start_mask = (start & -start) - 1;
uint64_t size_mask = pow2floor(size) - 1;
return MIN(MIN(size_mask, start_mask), max_mask) + 1;
Paolo
>> size = MIN(size, max_mask);
>> if (alignment <= size) {
>> /* Increase the alignment of start */
>> return alignment;
>> } else {
>> /* Find the largest page mask from size */
>> return 1ULL << (63 - clz64(size));
>> }
>>
>> Also please rename it to get_naturally_aligned_size.
>
> Will do. Thanks,
>
