Re: [Xen-devel] [PATCH] VMX: allocate APIC access page from domain heap

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Wednesday, December 16, 2015 3:58 PM
> 
> ... since we don't need its virtual address anywhere (it's a
> placeholder page only after all). For this wo work (and possibly be
> done elsewhere too) share_xen_page_with_guest() needs to mark pages
> handed to it as Xen heap ones.
> 
> To be on the safe side, also explicitly clear the page (not having done
> so was okay due to the XSA-100 fix, but is still a latent bug since we
> don't formally guarantee allocations to come out zeroed, and in fact
> this property may disappear again as soon as the asynchronous runtime
> scrubbing patches arrive).

Do you mean that asynchronous scrubbing may scrub page after they
are re-allocated? It's unrelated but a bit risky to me.

> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Alternatives might be to use a
> - global (or perhaps per-node) page across VMs (on the basis that VMs
>   shouldn't be writing into that page anyway)
> - fake MFN pointing into nowhere (would need to ensure no side effects
>   can occur, like PCIe errors or NMIs)

one page per VM should be fine. We don't need go that route.

the patch overall looks OK to me:

Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

Thanks
Kevin

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