Re: [PATCH v3 12/21] KVM: X86: Implement ring-based dirty memory tracking

[Paolo Bonzini]

On 21/01/20 09:29, Peter Xu wrote:
>>>> If we are short on bits we can just use 1 bit. E.g. set if
>>>> userspace has collected the GFN.
>>> I'm still unsure whether we can use only one bit for this.  Say,
>>> otherwise how does the userspace knows the entry is valid?  For
>>> example, the entry with all zeros ({.slot = 0, gfn = 0}) could be
>>> recognized as a valid dirty page on slot 0 gfn 0, even if it's
>>> actually an unused entry.
>> So I guess the reverse: valid entry has bit set, userspace sets it to
>> 0 when it collects it?
> Right, this seems to work.

Yes, that's okay too.

Paolo