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Date:      Mon, 7 Jun 2021 10:21:13 -0400
From:      Mark Johnston <markj@freebsd.org>
To:        Wei Hu <weh@microsoft.com>
Cc:        Harry Schmalzbauer <freebsd@omnilan.de>, "freebsd-virtualization@freebsd.org" <freebsd-virtualization@freebsd.org>
Subject:   Re: FreeBSD 12.1 i386 on Hyper-V Fails to Mount Root
Message-ID:  <YL4rWbNDi1p2hu4T@nuc>
In-Reply-To: <TYZP153MB0446D741558750B0216C1CF5BB3A9@TYZP153MB0446.APCP153.PROD.OUTLOOK.COM>
References:  <c6013e67-4a37-43e1-4452-568d3ef6e5a7@omnilan.de> <ef85f9bb-ad8b-978e-da65-c887e8e8498e@omnilan.de> <PSAP153MB0440FD09AD1981FD569B7246BB2D9@PSAP153MB0440.APCP153.PROD.OUTLOOK.COM> <YKIDX/PjOlNc%2BtMa@kib.kiev.ua> <PSAP153MB0440A1511904E54767BF5344BB2D9@PSAP153MB0440.APCP153.PROD.OUTLOOK.COM> <YKIRelPB9wmtBzzo@kib.kiev.ua> <22bbe4cd-82ed-b826-9ac0-05ef8aceba0e@omnilan.de> <7986b561-dd26-a134-e76d-530900363deb@omnilan.de> <fe59b52c-edb1-8c55-14fb-5d852826abe7@omnilan.de> <TYZP153MB0446D741558750B0216C1CF5BB3A9@TYZP153MB0446.APCP153.PROD.OUTLOOK.COM>

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On Sat, Jun 05, 2021 at 01:00:45PM +0000, Wei Hu via freebsd-virtualization wrote:
> Hi Harry,
> 
> Can you test if this patch fixes the problems?
> 
> https://reviews.freebsd.org/D30577

Hi Wei,

Harry tested the patch before I submitted the review; it does indeed fix
the problems with vmbus on i386/hyperv.

> > -----Original Message-----
> > From: Harry Schmalzbauer <freebsd@omnilan.de>
> > Sent: Friday, May 21, 2021 8:50 PM
> > To: Konstantin Belousov <kostikbel@gmail.com>; Wei Hu <weh@microsoft.com>
> > Cc: freebsd-virtualization@freebsd.org
> > Subject: Re: FreeBSD 12.1 i386 on Hyper-V Fails to Mount Root
> > 
> > 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)
> > 
> > Host CPU differs significantly though and I have no possibility to test this
> > influence.  Ther HyperV is Dual-Socket E5-2630 while the ESXi host is a single
> > socket X3470 Xeon (pre SandyBridge).
> > 
> > Maybe someone has an idea how this affects these symptoms.
> > 
> > Thanks,
> > -harry
> > 
> 
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