Account for dmap limit when selecting the pages for the bootstrap pagetables.

[kib]

Summary

physmap[] can be inconsistent with the physical memory limit due to buggy bios, or to the hw.physmem tunable. Since bootstrap pagetables are initialized by accesses through the DMAP, we must ensure that DMAP really cover the selected pages. This is only relevant when machine has less than 4G RAM and buggy BIOS, which is the combination on Acer Chromebook 720.

An alternative could be to always cover 4G for DMAP, but this change seems to be simpler.

[kib]

Rework the change as discussed with royger.

Michael, please retest.

[royger]

LGTM, just one nit.

sys/amd64/amd64/mp_machdep.c

125 ↗

(On Diff #43364)

I would use 'physmap[i + 1] > Maxmem', to make sure that all the pages used to build the page tables are below Maxmem, not just the initial one.

[kib]

Fix bug.

[grembo]

@kib Updated by tree to r334733 and applied the patch, it's working as expected, thanks!