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

[George Dunlap <george.dunlap@eu.citrix.com>]

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@citrix.com>
> Cc: Konrad Wilk <konrad.wilk@oracle.com>
> Cc: George Dunlap <george.dunlap@eu.citrix.com>
> Cc: Ian Campbell <ian.campbell@citrix.com>
> Cc: Ian Jackson <ian.jackson@eu.citrix.com>

Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>

> ---
> 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.

  -George