FreeBSD 12.1 i386 on Hyper-V Fails to Mount Root

[Harry Schmalzbauer]

Am 21.05.2021 um 14:50 schrieb Harry Schmalzbauer:
> Am 19.05.2021 um 13:26 schrieb Harry Schmalzbauer:
>
> ...
>> I can just assure that I tracked it down to the single r332489 
>> committ which makes vmbus(4) failing on i386.
>> Verification done:
>> - built/installed world&kernel on i386 HyV guest with r332488
>>   reboot fine.
>> - built/installed kernel on the same vm after svnlite up -r 332489
>>   reboot fails with "vmbus0: cannot find free IDT vector"
>> - loaded kernel.old/kernel, did revert 332489, by 'svnlite up -r 
>> 332488' and compiled/reinstalled kernel (again r332488)
>>   reboot fine.
>
> While having hard time catching up with x86 basics, I found another 
> oddity:
> On Hyper-V gen1, the maximum ammount of RAM I can assign a FreeBSD 
> guest beeing able to boot i386 is 3914MB, startring with r332489.
> As soon as I configure the guest to have 3916MB or more, FreeBSD-i386 
> r332489 booting leads to guest reset.  Loader starts kernel, machine 
> reboots.
> Either reverting to r332488 or reducing guest-RAM solves this.
>
> The most interesting fact here is that I couldn't reproduce it on ESXi.
> I ducplicated the Hyper-V HDD and started the exactly same code on 
> ESXi(v6) guest, where it doesn't crash!  I can boot FreeBSD-i386 
> r332489 with any ammount of guest-RAM on ESXi.
> (speaking for GENERIC, non-PAE)

Now that I have a living r332489 i386 available, I checked some sysctl.
It seems on ESXi and i386, large page mappings aren't used anymore, or 
is it just wrong indicating?

These valueas are suspicious to my eyes:

kern.version: FreeBSD 12.0-CURRENT #0 r332489: Fri May 21 15:32:35 CEST 2021
     root at esxtest:/usr/obj/altroot/usr/src/i386.i386/sys/GENERIC
hw.pagesizes: 4096 0
hw.realmem: 0
vm.min_kernel_address: 0
vm.max_kernel_address: 4286578688
vm.kvm_free: -549453824
vm.kvm_size: -16777216
vm.pmap.pg_ps_enabled: 0

kern.version: FreeBSD 12.0-CURRENT #1 r332488: Fri May 21 17:35:58 CEST 2021
     root at esxtest:/usr/obj/altroot/usr/src/i386.i386/sys/GENERIC
hw.pagesizes: 4096 4194304
hw.realmem: 0
vm.min_kernel_address: 3220172800
vm.max_kernel_address: 4294963200
vm.kvm_free: 624947200
vm.kvm_size: 1073737728
vm.pmap.pg_ps_enabled: 1

Thanks for any hints,
-harry