Re: [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian issues explicitly

Avi Kivity
2010-04-21T11:15:17Z

On 04/20/2010 02:00 PM, Takuya Yoshikawa wrote:
> We are now using generic___set_le_bit() to make dirty bitmaps le.
> Though this works well, we have to replace __set_bit() to appropriate
> uaccess function to move dirty bitmaps to user space. So this patch
> splits generic___set_le_bit() and prepares for that.
>
>
> +static int __mark_page_dirty(unsigned long nr,
> + unsigned long *dirty_bitmap)
> +{
> +#ifdef __BIG_ENDIAN
> + nr = nr ^ BITOP_LE_SWIZZLE;
> +#endif
> + __set_bit(nr, dirty_bitmap);
>

Why not introduce __set_le_bit_user() along with __set_bit_user()? kvm
shouldn't do endian corrections when they can be done in generic code.

> +}
> +
> void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
> {
> struct kvm_memory_slot *memslot;
> @@ -1203,11 +1212,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
> if (memslot&& memslot->dirty_bitmap) {
> unsigned long rel_gfn = gfn - memslot->base_gfn;
>
> - /* avoid RMW */
> - if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap)) {
> - generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
> - memslot->is_dirty = true;
> - }
>

You're also dropping the RMW avoidance. This is fine, but deserves at
least a note in the changelog (or a separate patch).

> + __mark_page_dirty(rel_gfn, memslot->dirty_bitmap);
> + memslot->is_dirty = true;
> }
> }
>
>

--
error compiling committee.c: too many arguments to function