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

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

Anthony Liguori wrote:
> Avi Kivity wrote:
>> It depends on what's going on?  Does a page table point to mmio?  Or 
>> the glommerclock?
>>
>> Not sure there is a single answer.
>>
>>> Perhaps we should be replacing consumers of gfn_to_page() with 
>>> copy_to_user() instead?
>>
>> Indeed we should.  The problem is access in atomic contexts.  It's 
>> easy to detect failure, but not always easy to handle it.
>
> So I think we should replace it with a rate limited printk and 
> returning bad_page.  That way the guest can't exploit it and we'll 
> still hopefully get printk()s to track down instances of things going 
> bad.
>

Agreed.  Add a stacktrace so we can see what causes the badness.

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