[Xen-devel] RE: [RFC][PATCH] Basic support for page offline

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Tim Deegan <mailto:Tim.Deegan@xxxxxxxxxx> wrote:
> Hi,
> 
> At 14:51 +0000 on 18 Feb (1234968681), Jiang, Yunhong wrote:
>> Can you please share me which existing PET-updating code? I browsed
>> the code and didn't find approprate function, especially considering
>> we need update all level page tables.
> 
> xen/arch/x86/mm.c: mod_l1_entry() mod_l2_entry(), etc.

Yes, I considered this also, I give it up because these function will do more 
than simply swap the entry, for example, it may try to re-validate the page 
table again. But yes, I should use them because they are common function and 
performance is not important for us.

> It should be possible to have the tools do all the PTE manipulations
> with MMU update hypercalls (I think -- Keir may correct me here). Then
> the final hypercall to surrender the page will fail if the grant tables
> are wrong; if it does, put the PTEs back and fall back to a live
> migration.  Isn't that what your in-xen code does anyway?

Yes, although we may need a very big multicall to achieve it. I didn't see any 
issue with this method and will work this way.

BTW, I think what we are doing is in fact something like memory_exchange(), 
although memory_exchange() requires the source memory is not referenced anymore.

Thanks
Yunhong Jiang

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