linux-kernel - Re: [PATCH v5 1/9] MIPS: Avoid future duplicate elf core header reservation

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Date:   Mon, 23 Aug 2021 16:09:47 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Nick Kossifidis <mick@....forth.gr>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Frank Rowand <frowand.list@...il.com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        kexec@...ts.infradead.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/9] MIPS: Avoid future duplicate elf core header
 reservation

On Mon, Aug 23, 2021 at 12:17:50PM +0200, Geert Uytterhoeven wrote:
> Hi Mike,
> 
> On Mon, Aug 16, 2021 at 7:52 AM Mike Rapoport <rppt@...nel.org> wrote:
> > On Wed, Aug 11, 2021 at 10:50:59AM +0200, Geert Uytterhoeven wrote:
> > > Prepare for early_init_fdt_scan_reserved_mem() reserving the memory
> > > occupied by an elf core header described in the device tree.
> > > As arch_mem_init() calls early_init_fdt_scan_reserved_mem() before
> > > mips_reserve_vmcore(), the latter needs to check if the memory has
> > > already been reserved before.
> >
> > Doing memblock_reserve() for the same region is usually fine, did you
> > encounter any issues without this patch?
> 
> Does it also work if the same region is part of an earlier larger
> reservation?  I am no memblock expert, so I don't know.
> I didn't run into any issues, as my MIPS platform is non-DT, but I
> assume arch/arm64/mm/init.c:reserve_elfcorehdr() had the check for
> a reason.

The memory will be reserved regardless of the earlier reservation, the
issue may appear when the reservations are made for different purpose. E.g.
if there was crash kernel allocation before the reservation of elfcorehdr.

The check in such case will prevent the second reservation, but, at least
in arch/arm64/mm/init.c:reserve_elfcorehdr() it does not seem to prevent
different users of the overlapping regions to step on each others toes.

Moreover, arm64::reserve_elfcorehdr() seems buggy to me, because of there
is only a partial overlap of the elfcorehdr with the previous reservation,
the non-overlapping part of elfcorehdr won't get reserved at all.

> Thanks!
> 
> >
> > > Note that mips_reserve_vmcore() cannot just be removed, as not all MIPS
> > > systems use DT.
> > >
> > > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > > ---
> > > v5:
> > >   - New.
> > > ---
> > >  arch/mips/kernel/setup.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> > > index 23a140327a0bac1b..4693add05743d78b 100644
> > > --- a/arch/mips/kernel/setup.c
> > > +++ b/arch/mips/kernel/setup.c
> > > @@ -429,7 +429,8 @@ static void __init mips_reserve_vmcore(void)
> > >       pr_info("Reserving %ldKB of memory at %ldKB for kdump\n",
> > >               (unsigned long)elfcorehdr_size >> 10, (unsigned long)elfcorehdr_addr >> 10);
> > >
> > > -     memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
> > > +     if (!memblock_is_region_reserved(elfcorehdr_addr, elfcorehdr_size)
> > > +             memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
> > >  #endif
> > >  }
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

-- 
Sincerely yours,
Mike.