Re: [Xen-devel] [PATCH 01/18] xen: reinstate previously unused XENMEM_remove_from_physmap hypercall

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 01/18/2012 05:36 AM, Ian Campbell wrote:
> On Thu, 2012-01-12 at 23:35 +0000, Daniel De Graaf wrote:
>> From: Alex Zeffertt <alex.zeffertt@xxxxxxxxxxxxx>
>>
>> This patch reinstates the XENMEM_remove_from_physmap hypercall
>> which was removed in 19041:ee62aaafff46 because it was not used.
>>
>> However, is now needed in order to support xenstored stub domains.
>> The xenstored stub domain is not priviliged like dom0 and so cannot
>> unilaterally map the xenbus page of other guests into it's address
>> space.  Therefore, before creating a domU the domain builder needs to
>> seed its grant table with a grant ref allowing the xenstored stub
>> domain to access the new domU's xenbus page.
>>
>> At present domU's do not start with their grant table mapped.
>> Instead it gets mapped when the guest requests a grant table from
>> the hypervisor.
>>
>> In order to seed the grant table, the domain builder first needs to
>> map it into dom0 address space.  But the hypercall to do this
>> requires a gpfn (guest pfn), which is an mfn for PV guest, but a pfn
>> for HVM guests.  Therfore, in order to seed the grant table of an
>> HVM guest, dom0 needs to *temporarily* map it into the guest's
>> "physical" address space.
>>
>> Hence the need to reinstate the XENMEM_remove_from_physmap hypercall.
>>
>> Signed-off-by: Alex Zeffertt <alex.zeffertt@xxxxxxxxxxxxx>
>> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> 
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx> (modulo Jan's comment
> about ordering in xlat.lst)
> 
> BTW, since Alex and Diego have subsequently left Citrix you could take
> my Acked-by's in this series as Signed-of-by on behalf of Citrix. I've
> no idea if that's necessary though, I expect not.
> 
> Ian.
> 

I'm not an expert in this area, but this is how I read it: the portion of
the path authored by Alex/Diego was already signed-off when they were posted,
so since the current patches are derived works from them the sign-off may
need to stay in order to allow me to sign off because I cannot claim copyright
on all of the content. Assuming Citrix actually owns the copyright on the
patches, your Ack may suffice to replace the sign-off for this purpose.

I guess my real question here would be: should the sign-off from Alex and
Diego remain on these patches in addition to your Ack?


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