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David Vrabel authored
The patch "xen: use maximum reservation to limit amount of usable RAM" (d312ae87) breaks machines that do not use 'dom0_mem=' argument with: reserve RAM buffer: 000000133f2e2000 - 000000133fffffff (XEN) mm.c:4976:d0 Global bit is set to kernel page fffff8117e (XEN) domain_crash_sync called from entry.S (XEN) Domain 0 (vcpu#0) crashed on cpu#0: ... The reason being that the last E820 entry is created using the 'extra_pages' (which is based on how many pages have been freed). The mentioned git commit sets the initial value of 'extra_pages' using a hypercall which returns the number of pages (if dom0_mem has been used) or -1 otherwise. If the later we return with MAX_DOMAIN_PAGES as basis for calculation: return min(max_pages, MAX_DOMAIN_PAGES); and use it: extra_limit = xen_get_max_pages(); if (extra_limit >= max_pfn) extra_pages = extra_limit - max_pfn; else extra_pages = 0; which means we end up with extra_pages = 128GB in PFNs (33554432) - 8GB in PFNs (2097152, on this specific box, can be larger or smaller), and then we add that value to the E820 making it: Xen: 00000000ff000000 - 0000000100000000 (reserved) Xen: 0000000100000000 - 000000133f2e2000 (usable) which is clearly wrong. It should look as so: Xen: 00000000ff000000 - 0000000100000000 (reserved) Xen: 0000000100000000 - 000000027fbda000 (usable) Naturally this problem does not present itself if dom0_mem=max:X is used. CC: stable@kernel.org Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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