[Xen-devel] tmem and construct_dom0 memory allocation race

[Dulloor <dulloor@xxxxxxxxx>]

tmem could cause Dom0 allocation to fail with error "Not enough RAM
for DOM0 reservation", particularly when used without dom0_mem option.

Following is the sequence :
- init_tmem allocates a set of pages and sets up dstmem and workmem to
alloc pages in MP case (with cpu notifiers)
- construct_dom0 estimates nr_pages by calling avail_domheap_pages
- On other CPUs, tmem cpu_notifier gets called and allocates pages
from domheap, making the construct_dom0's estimate stale.
- construct_dom0 fails

tmem=off or dom0_mem=xxx both solve the problem for now.

-dulloor

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