Re: [PATCH v11 10/12] vduse: Implement an MMU-based software IOTLB

[Yongji Xie]

On Fri, Aug 27, 2021 at 4:53 PM John Garry <john.garry@xxxxxxxxxx> wrote:
>
> On 18/08/2021 13:06, Xie Yongji wrote:
> > +
> > +static dma_addr_t
> > +vduse_domain_alloc_iova(struct iova_domain *iovad,
> > +                     unsigned long size, unsigned long limit)
> > +{
> > +     unsigned long shift = iova_shift(iovad);
> > +     unsigned long iova_len = iova_align(iovad, size) >> shift;
> > +     unsigned long iova_pfn;
> > +
> > +     /*
> > +      * Freeing non-power-of-two-sized allocations back into the IOVA caches
> > +      * will come back to bite us badly, so we have to waste a bit of space
> > +      * rounding up anything cacheable to make sure that can't happen. The
> > +      * order of the unadjusted size will still match upon freeing.
> > +      */
> > +     if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1)))
> > +             iova_len = roundup_pow_of_two(iova_len);
>
> Whether it's proper to use this "fast" API or not here, this seems to be
> copied verbatim from dma-iommu.c, which tells me that something should
> be factored out.
>

Agreed.

> Indeed, this rounding up seems a requirement of the rcache, so not sure
> why this is not done there.
>

Me too. I guess it is to let users know that space is wasted.

Thanks,
Yongji