Re: [Qemu-devel] [PATCH 2/2] intel_iommu: Fix unexpected unmaps during global unmap

[Paolo Bonzini <pbonzini@redhat.com>]

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.

> +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;

    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.

Paolo