Re: [Xen-devel] [PATCH 3/3] x86_64: allow more vCPU-s per guest

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 18.06.09 11:39 >>>
> Then I think it would be better to make that domctl really singleshot (i.e.,
> fail if d->max_vcpus is already non-zero), with a comment explaining why it
> is implemented this way. Buggily implementing an unused case can't be good.
> Can you generate a patch for this, please?

Here we go:

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2009-06-10.orig/xen/common/domctl.c 2009-06-10 15:04:45.000000000 +0200
+++ 2009-06-10/xen/common/domctl.c      2009-06-18 13:48:30.000000000 +0200
@@ -463,6 +463,16 @@ long do_domctl(XEN_GUEST_HANDLE(xen_domc
         if ( (max < d->max_vcpus) && (d->vcpu[max] != NULL) )
             goto maxvcpu_out;
 
+        /*
+         * For now don't allow increasing the vcpu count from a non-zero
+         * value: This code and all readers of d->vcpu would otherwise need
+         * to be converted to use RCU, but at present there's no tools side
+         * code path that would issue such a request.
+         */
+        ret = -EBUSY;
+        if ( (d->max_vcpus > 0) && (max > d->max_vcpus) )
+            goto maxvcpu_out;
+
         ret = -ENOMEM;
         if ( max > d->max_vcpus )
         {




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