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From: John Baldwin <jhb@freebsd.org>
To: Alan Cox <alc@rice.edu>
Cc: Bryan Drewery <bdrewery@freebsd.org>, src-committers@freebsd.org,
 svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject: Re: svn commit: r319702 - head/sys/vm
Date: Thu, 08 Jun 2017 15:28 -0700
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On Thursday, June 08, 2017 05:07:40 PM Alan Cox wrote:
>=20
> > On Jun 8, 2017, at 2:37 PM, John Baldwin <jhb@freebsd.org> wrote:
> >=20
> > On Thursday, June 08, 2017 12:55:45 PM Bryan Drewery wrote:
> >> On 6/8/17 12:18 PM, John Baldwin wrote:
> >>> Author: jhb
> >>> Date: Thu Jun  8 16:18:41 2017
> >>> New Revision: 319702
> >>> URL: https://svnweb.freebsd.org/changeset/base/319702
> >>>=20
> >>> Log:
> >>>  Fix an off-by-one error in the VM page array on some systems.
> >>>=20
> >>>  r31386 changed how the size of the VM page array was calculated =
to be
> >>>  less wasteful.=20
> >>=20
> >> r313186
> >=20
> > Oops.  FWIW, this commit fixes a reliable panic booting mips and mi=
ps64
> > kernels under qemu.  Adrian also reported the same panic on real mi=
ps
> > hardware.
> >=20
>=20
> Any architecture on which we don=E2=80=99t have superpage reservation=
s enabled could experience the panic at boot time.  Amd64, arm, arm64, =
i386, and sparc64 would never panic because of the memory allocated for=
 the reservation array.=20

Even then it seems to not be guaranteed.  The original change has
been in CheriBSD for a while, and we have not seen any panics on boot u=
nder
qemu as I saw with plain FreeBSD probably due to slightly different ear=
ly
memory allocations.

--=20
John Baldwin