Re: [Xen-devel] [PATCH] libxc: fix claim mode when creating HVM guest

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-01-27 at 19:09 +0000, George Dunlap wrote:
> On 01/27/2014 05:53 PM, Wei Liu wrote:
> > The original code is wrong because:
> > * claim mode wants to know the total number of pages needed while
> >    original code provides the additional number of pages needed.
> > * if pod is enabled memory will already be allocated by the time we try
> >    to claim memory.
> >
> > So the fix would be:
> > * move claim mode before actual memory allocation.
> > * pass the right number of pages to hypervisor.
> >
> > The "right number of pages" should be number of pages of target memory
> > minus VGA_HOLE_SIZE, regardless of whether PoD is enabled.
> >
> > This fixes bug #32.
> >
> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Cc: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
> > Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> > Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> 
> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

> 
> > ---
> > WRT 4.4 release: this patch should be accpeted, otherwise PoD + claim
> > mode is complete broken. If this patch is deemed too complicated, we
> > should flip the switch to disable claim mode by default for 4.4.
> 
> I think a more reasonable mitigation strategy would simply be to ignore 
> claim mode when constructing a domain that uses PoD.
> 
> I'm inclined to take this one.  Since claim mode is on by default, the 
> currently-working path should get exercised well before the release to 
> shake out any bugs.  The other path doesn't work at all currently 
> (AFAICT) unless you disable claim mode -- which is still available as a 
> work-around, even if there is a bug in this patch.
> 
> I'll wait a day or two for others to speak up before giving it a formal 
> ack, just in case.

I agree with this plan.

Ian.


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