update_va_mapping failing on recent core i7 980X

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

Hi list,

I am currently trying to boot an amd64 dom0 kernel (5.0, 5.1, current) 
with Xen 3.3 on a recent core i7 980X host (with 6GiB RAM).

Thing is, boot fails very early, in pmap_prealloc_lowmem_ptps(). At 
level == 4 (first iteration in the loop), the:

...
avail_start += PAGE_SIZE;
HYPERVISOR_update_va_mapping ((vaddr_t)early_zerop,
                    xpmap_ptom_masked(newp) | PG_u | PG_V | PG_RW, 
UVMF_INVLPG);
...

code seems to cause some sort of fault at hypervisor level, leading to 
a reboot. Made some checks in order to see that there is no dangling 
pointer (for phys_to_machine table, or uninitialized variable), and all 
the values seem to be sane (well, they have correct values).

The hypercall does not even return from hypervisor. Tried booting by 
limiting phys memory to 3GiB (mem=3G passed to xen): it does not change 
the outcome.

Does this ring a bell to someone before I dig further?

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost