Re: [Xen-devel] [PATCH 01/10] VMX: Enable EPT A/D bit support

[Kai Huang <kai.huang@xxxxxxxxxxxxxxx>]

On 04/10/2015 04:54 PM, Tim Deegan wrote:
> At 14:40 +0800 on 10 Apr (1428676858), Kai Huang wrote:
> > > In fact, thinking about that, we should probably be setting _all_ the
> > > A bits to 1, even in leaf entries, to avoid the overhead of the MMU
> > > having to write them later.
> > I suppose you mean A bits of leaf entries of new shattered 4K pages? Yes
> > we can, but looks it's more reasonable to inherit according to original
> > A bit of super page.
> Yes, inheriting is best, but we should have already set the A bit of the
> superpage to 1 as well, for the same reasons.  IOW we should set every A
> bit in the whole system to 1 all the time.
>
> BTW, this is what we do with A/D bits in normal pagetables in Xen too
> -- the default is to set them all the time, so the MMU doesn't have to
> fix them up later.
Sure then we can set all A bit to 1, which can be done by setting A bit 
properly in ept_p2m_type_to_flags I think.
What does normal pagetables mean here? I don't think you mean shadow 
page table, as shadow page table needs to sync A/D bits with guest 
table, right?
Thanks,
-Kai
> Cheers,
>
> Tim.

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