Re: [kvm-devel] [PATCH] Handle vma regions with no backing page (v2)

[Avi K. <av...@qu...>]

Anthony Liguori wrote:
> This patch allows VMA's that contain no backing page to be used for guest
> memory.  This is a drop-in replacement for Ben-Ami's first page in his direct
> mmio series.  Here, we continue to allow mmio pages to be represented in the
> rmap.
>
>   

I like this very much, as it only affects accessors and not the mmu core 
itself.

Hollis/Xiantao/Carsten, can you confirm that this approach works for 
you?  Carsten, I believe you don't have mmio, but at least this 
shouldn't interfere.

>  
>  struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
>  {
> -	return pfn_to_page(gfn_to_pfn(kvm, gfn));
> +	pfn_t pfn;
> +
> +	pfn = gfn_to_pfn(kvm, gfn);
> +	if (pfn_valid(pfn))
> +		return pfn_to_page(pfn);
> +
> +	return NULL;
>  }
>   

You're returning NULL here, not bad_page.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.