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



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>

---
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

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