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Re: [Xen-devel] [PATCH for-xen-4.5] libxl: Allow copying smaller bitmap into a larger one



On 11/25/2014 06:41 AM, Dario Faggioli wrote:
On Tue, 2014-11-25 at 11:15 +0000, Wei Liu wrote:
And here it is.

Boris, can you give it a shot?

---8<---
 From 77531e31d239887b9f36c03e434300bc30683092 Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Tue, 25 Nov 2014 10:59:47 +0000
Subject: [PATCH] libxl: allow copying between bitmaps of different sizes

When parsing bitmap objects JSON parser will create libxl_bitmap map of the
smallest size needed.

This can cause problems when saved image file specifies CPU affinity.  For
example, if 'vcpu_hard_affinity' in the saved image has only the first CPU
specified, just a single byte will be allocated and libxl_bitmap->size will be
set to 1.

This will result in assertion in libxl_set_vcpuaffinity()->libxl_bitmap_copy()
since the destination bitmap is created for maximum number of CPUs.

We could allocate that bitmap of the same size as the source, however, it is
later passed to xc_vcpu_setaffinity() which expects it to be sized to the max
number of CPUs

To fix this issue, introduce an internal function to allowing copying between
bitmaps of different sizes. Note that this function is only used in
libxl_set_vcpuaffinity at the moment. Though NUMA placement logic invoke
libxl_bitmap_copy as well there's no need to replace those invocations.  NUMA
placement logic comes into effect when no vcpu / node pinning is provided, so
it always operates on bitmap of the same sizes (that is, size of maximum
number of cpus /nodes).

Reported-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>

If this end up being the approach, it can have the following:

Reviewed-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>

Tested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>



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