[Xen-devel] RE: [RFC][PATCH]Large Page Support for HAP

["Huang2, Wei" <Wei.Huang2@xxxxxxx>]

Tim Deegan wrote:
> Hi,
> 
> At 10:26 -0600 on 15 Nov (1195122365), Huang2, Wei wrote:
>> 2. Shadow paging
>> - This implementation will affect shadow mode, especially at
>> xc_hvm_build.c and memory.c. 
>> - Where and how to avoid affecting shadow?
> 
> Shadow already uses SH_LINEAR_PT_VIRT_START, so we can't put a
> mapping there.  

Given that we don't use SH_LINEAR_PT_VIRT_START in current HAP mode, I
think it is OK to borrow this address space for HAP. You are right that
Shadow is using it; so it is a bit dangerous. If we can prevent large
page support in shadow paging, is using SH_LINEAR_PT still acceptable
for you?

> Can you just use the normal linear mapping plus the
> RO_MPT mapping of the p2m instead?  
> 
> Otherwise, the only thing I can see that shadow will need is for the
> callback from the p2m code that writes the entries to be made aware
> of the superpage level-2 entries.  It'll need to treat a superpage
> entry the same way as 512/1024 level-1 entries.   


Could you elaborate on this idea? RO_MPT is currently being used. I did
not see any spare linear space I can borrow except SH_LINEAR_PT. Do you
mean I can still borrow it, but have to handle it correctly in shadow
code if it is a super page?


Thanks,

-Wei

> 
> Cheers,
> 
> Tim.



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