From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@qumranet.com>
Subject: Re: [PATCH] Handle vma regions with no backing page (v2)
Date: Wed, 30 Apr 2008 01:17:49 +0300
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Cc: Carsten Otte <cotte@de.ibm.com>,
	Andrea Arcangeli <andrea@qumranet.com>,
	Hollis Blanchard <hollisb@us.ibm.com>,
	kvm-devel@lists.sourceforge.net, Ben-Ami Yassour <benami@il.ibm.com>,
	"Zhang,  Xiantao" <xiantao.zhang@intel.com>
To: Anthony Liguori <aliguori@us.ibm.com>
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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.


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