Re: 32bit kernel is broken for Linux-5.1-rc1 due to GCC cmodel=medlow

[Anup Patel <anup@brainfault.org>]

On Fri, Mar 22, 2019 at 6:55 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Fri, Mar 22, 2019 at 12:42:10PM +0200, Mike Rapoport wrote:
> > Hi,
> >
> > On Fri, Mar 22, 2019 at 11:46:24AM +0530, Anup Patel wrote:
> > > Hi Palmer,
> > >
> > > The 32bit kernel booting is broken for Linux-5.1-rc1 due to GCC cmodel=medlow
> > > affecting setup_vm() movement from kernel/setup.c to mm/init.c.
> > >
> > > There is no issue with 64bit kernel booting.
> > >
> > > The "[PATCH v2 2/5] RISC-V: Make setup_vm() independent of GCC code model"
> > > fixes this issue.
> > >
> > > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1959102.html
> > >
> > > If possible please include above patch as Linux-5.1-rc1 fix.
> >
> > I'm not convinced that it's the best solution. Multiple __load_pa() and
> > __load_va() conversions make code unreadable.
> > Is there any reason swapper_pg_dir cannot be setup after 'relocate'? It'll
> > save a lot of churn for the current fix and for the addition of 4K mappings
>
> I think for 5.1-rc we should just revert the cleanup patch ASAP until
> we figure out what else we want to do.

I think reverting is not right way to go here because there is deeper issue
in using GCC cmodel=medlow with setup_vm() which is called from assembly
with MMU off.

Even if we keep setup_vm() in kernel/setup.c then still in-future it can break
for 32bit system as more code gets added to kernel/setup.c.

The setup_vm() should not be sensitive to which source file it is placed in.
The patch which breaks 32bit kernel just moves setup_vm() from
kernel/setup.c to mm/init.c.

Regards,
Anup

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