[Xen-devel] RE: [PATCH] Support swap a page from user space tools -- Was RE: [RFC][PATCH] Basic support for page offline

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

Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> On 19/03/2009 13:01, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
> 
>> Instead of add a new mmu_*op, I try to change the MMU_NORMAL_PT_UPDATE to
>> support update foreign page table. There will be some restirction for it,
>> including the pagetable and the new mfn pointed should be owned by same
>> domain, and the domain should be suspeneded already. The
>> update_foregin_pt.patch is for this. I'm not sure if this method is
>> feasible. 
> 
> I'll need to look in more detail, but yes it does appear this
> approach can
> work. This is probably the easiest way to go in that case.
> 
>> The exchange_page.patch is to replace a mfn with a new one. Although there
>> is already a memory_exchange hypercall, but that hypercall will not accept
>> new page, add that support will break current ABI. Also it does not support
>> foreign domain. This function add those support
> 
> Well, why is the existing hypercall not okay by itself? Why
> can you not take
> an arbitrary new mfn and you feel you have to specify it from the tools
> instead? 

It is ok for us to use an arbitrary new mfn, and then do the update_entry. But 
what happen if this process failed and we want to turn back to the old page? We 
still need this mechanism at that situation.

Thanks
Yunhong Jiang

> 
> -- Keir
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