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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-01-18 at 14:56 +0000, Daniel De Graaf wrote:
> 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,

Me neither.

> 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 don't think an Ack conveys the same meaning (WRT the DCO) as a
Signed-off-by.

> 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?

I would suggest you keep any signed-off-by they provided and augment it
with my ack. 

I think I saw one or two which said "Originally-by" instead of
"Signed-of-by", I guess those were either missing a Signed-off-by in the
first place or have been heavily modified?

Ian.

> 



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