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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Tue, 14 Jun 2022 12:27:15 +0200
Message-ID: <CAMj1kXGXvjrnY=Hzd4c3CYZsNT6OiqTcMmKT0tdnk=jFOiVpWA@mail.gmail.com>
Subject: Re: [PATCH v5 5/5] memblock: Disable mirror feature if kernelcore is
 not specified
To:     Baoquan He <bhe@redhat.com>
Cc:     Wupeng Ma <mawupeng1@huawei.com>, Jonathan Corbet <corbet@lwn.net>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Kees Cook <keescook@chromium.org>, songmuchun@bytedance.com,
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        Robin Murphy <robin.murphy@arm.com>,
        David Hildenbrand <david@redhat.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Zhen Lei <thunder.leizhen@huawei.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, gpiccoli@igalia.com,
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On Tue, 14 Jun 2022 at 12:20, Baoquan He <bhe@redhat.com> wrote:
>
> On 06/14/22 at 05:21pm, Wupeng Ma wrote:
> > From: Ma Wupeng <mawupeng1@huawei.com>
> >
> > If system have some mirrored memory and mirrored feature is not specified
> > in boot parameter, the basic mirrored feature will be enabled and this will
> > lead to the following situations:
> >
> > - memblock memory allocation prefers mirrored region. This may have some
> >   unexpected influence on numa affinity.
> >
> > - contiguous memory will be split into several parts if parts of them
> >   is mirrored memory via memblock_mark_mirror().
> >
> > To fix this, variable mirrored_kernelcore will be checked in
> > memblock_mark_mirror(). Mark mirrored memory with flag MEMBLOCK_MIRROR iff
> > kernelcore=mirror is added in the kernel parameters.
> >
> > Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
> > Acked-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  mm/internal.h   | 2 ++
> >  mm/memblock.c   | 3 +++
> >  mm/page_alloc.c | 2 +-
> >  3 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/internal.h b/mm/internal.h
> > index c0f8fbe0445b..ddd2d6a46f1b 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -861,4 +861,6 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags);
> >
> >  DECLARE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
> >
> > +extern bool mirrored_kernelcore;
> > +
> >  #endif       /* __MM_INTERNAL_H */
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index b1d2a0009733..a9f18b988b7f 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -924,6 +924,9 @@ int __init_memblock memblock_clear_hotplug(phys_addr_t base, phys_addr_t size)
> >   */
> >  int __init_memblock memblock_mark_mirror(phys_addr_t base, phys_addr_t size)
> >  {
> > +     if (!mirrored_kernelcore)
> > +             return 0;
>
> memblock_mark_mirror() is just a wrapper, maybe we should check this in
> efi_find_mirror(). Otherwise, how do we explain the message printed out
> at below in boot log if we don't mark mirror memory at all?
>
> void __init efi_find_mirror(void)
> {
> ......
>         if (mirror_size)
>                 pr_info("Memory: %lldM/%lldM mirrored memory\n",
>                         mirror_size>>20, total_size>>20);
> }
>

EFI does not care about *how* mirrored memory is being used or not, it
just reports what the firmware provided. So EFI is not the appropriate
level to take kernelcore=mirror into account.

I already mentioned that memblock_mark_mirror() is also the wrong
place IMO, but Kefeng explained that doing it elsewhere is
problematic.