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Date:   Wed, 5 Sep 2018 21:37:52 +0300
From:   Mike Rapoport <rppt@linux.vnet.ibm.com>
To:     Paul Burton <paul.burton@mips.com>
Cc:     Serge Semin <fancer.lancer@gmail.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        James Hogan <jhogan@kernel.org>,
        Huacai Chen <chenhc@lemote.com>,
        Michal Hocko <mhocko@kernel.org>, linux-mips@linux-mips.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND] mips: switch to NO_BOOTMEM
References: <1535356775-20396-1-git-send-email-rppt@linux.vnet.ibm.com>
 <20180830214856.cwqyjksz36ujxydm@pburton-laptop>
 <20180831211747.GA31133@rapoport-lnx>
 <20180905174709.pz2rmyt2oob6bxpz@pburton-laptop>
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On Wed, Sep 05, 2018 at 10:47:10AM -0700, Paul Burton wrote:
> Hi Mike,
> 
> On Sat, Sep 01, 2018 at 12:17:48AM +0300, Mike Rapoport wrote:
> > On Thu, Aug 30, 2018 at 02:48:57PM -0700, Paul Burton wrote:
> > > On Mon, Aug 27, 2018 at 10:59:35AM +0300, Mike Rapoport wrote:
> > > > MIPS already has memblock support and all the memory is already registered
> > > > with it.
> > > > 
> > > > This patch replaces bootmem memory reservations with memblock ones and
> > > > removes the bootmem initialization.
> > > > 
> > > > Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
> > > > ---
> > > > 
> > > >  arch/mips/Kconfig                      |  1 +
> > > >  arch/mips/kernel/setup.c               | 89 +++++-----------------------------
> > > >  arch/mips/loongson64/loongson-3/numa.c | 34 ++++++-------
> > > >  arch/mips/sgi-ip27/ip27-memory.c       | 11 ++---
> > > >  4 files changed, 33 insertions(+), 102 deletions(-)
> > > 
> > > Thanks for working on this. Unfortunately it breaks boot for at least a
> > > 32r6el_defconfig kernel on QEMU:
> > > 
> > >   $ qemu-system-mips64el \
> > >     -M boston \
> > >     -kernel arch/mips/boot/vmlinux.gz.itb \
> > >     -serial stdio \
> > >     -append "earlycon=uart8250,mmio32,0x17ffe000,115200 console=ttyS0,115200 debug memblock=debug mminit_loglevel=4"
> > >   [    0.000000] Linux version 4.19.0-rc1-00008-g82d0f342eecd (pburton@pburton-laptop) (gcc version 8.1.0 (GCC)) #23 SMP Thu Aug 30 14:38:06 PDT 2018
> > >   [    0.000000] CPU0 revision is: 0001a900 (MIPS I6400)
> > >   [    0.000000] FPU revision is: 20f30300
> > >   [    0.000000] MSA revision is: 00000300
> > >   [    0.000000] MIPS: machine is img,boston
> > >   [    0.000000] Determined physical RAM map:
> > >   [    0.000000]  memory: 10000000 @ 00000000 (usable)
> > >   [    0.000000]  memory: 30000000 @ 90000000 (usable)
> > >   [    0.000000] earlycon: uart8250 at MMIO32 0x17ffe000 (options '115200')
> > >   [    0.000000] bootconsole [uart8250] enabled
> > >   [    0.000000] memblock_reserve: [0x00000000-0x009a8fff] setup_arch+0x224/0x718
> > >   [    0.000000] memblock_reserve: [0x01360000-0x01361ca7] setup_arch+0x3d8/0x718
> > >   [    0.000000] Initrd not found or empty - disabling initrd
> > >   [    0.000000] memblock_virt_alloc_try_nid: 7336 bytes align=0x40 nid=-1 from=0x00000000 max_addr=0x00000000 early_init_dt_alloc_memory_arch+0x20/0x2c
> > >   [    0.000000] memblock_reserve: [0xbfffe340-0xbfffffe7] memblock_virt_alloc_internal+0x120/0x1ec
> > >   <hang>
> > > 
> > > It looks like we took a TLB store exception after calling memset() with
> > > a bogus address from memblock_virt_alloc_try_nid() or something inlined
> > > into it.
> > 
> > Memblock tries to allocate from the top and the resulting address ends up
> > in the high memory. 
> > 
> > With the hunk below I was able to get to "VFS: Cannot open root device"
> > 
> > diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> > index 4114d3c..4a9b0f7 100644
> > --- a/arch/mips/kernel/setup.c
> > +++ b/arch/mips/kernel/setup.c
> > @@ -577,6 +577,8 @@ static void __init bootmem_init(void)
> >          * Reserve initrd memory if needed.
> >          */
> >         finalize_initrd();
> > +
> > +       memblock_set_bottom_up(true);
> >  }
> 
> That does seem to fix it, and some basic tests are looking good.

The bottom up mode has the downside of allocating memory below
MAX_DMA_ADDRESS. 

I'd like to check if memblock_set_current_limit(max_low_pfn) will also fix
the issue, at least with the limited tests I can do with qemu.

> I notice you submitted this as part of your larger series to remove
> bootmem - are you still happy for me to take this one through mips-next?

Sure, I've just posted it as the part of the larger series for completeness.

I believe that in the next few days I'll be able to verify whether
memblock_set_current_limit() can be used instead of
memblock_set_bottom_up() and I'll resend the patch then.

> Thanks,
>     Paul
> 

-- 
Sincerely yours,
Mike.