Re: [Xen-devel] [PATCH RFC v2 1/4] x86/mm: Shadow and p2m changes for PV mem_access

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.08.14 at 18:56, <aravindp@xxxxxxxxx> wrote:
> Just to be certain as to where we stand:
> 
> 1. The "page table RW bit flipping" solution is not viable because pausing 
> the domain synchronously takes too long for many vcpus domains. Plus there is 
> the added issue of vcpu vs domain heuristics. This is the case even after 
> solving the page boundary and multiple page copy issues.
> 
> 2. The "CR0.WP with interrupts disabled" solution is not viable because of 
> NMIs. Or did I misunderstand?

For this second option, NMIs are a concern. Whether that makes it
not viable I'm not certain. We really need to weigh benefits and risks
here, and from a project wide perspective I'm currently viewing the
PV mem-access feature as a niche thing, the more that I'm unaware
of really wide spread use if HVM mem-access capabilities. I.e. the
most I can currently see happening is for it to go in clearly marked
experimental, provided that no code path used outside of that
feature suffers in any way (functionality and performance). But of
course I'm open to be convinced otherwise, or overruled by a
majority of other maintainers.

Jan


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