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Date:   Tue, 21 Aug 2018 15:07:25 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        G Gregory <graeme.gregory@...aro.org>, al.stone@...aro.org,
        bhsharma@...hat.com, tbaicar@...eaurora.org,
        kexec@...ts.infradead.org, lkml <linux-kernel@...r.kernel.org>,
        james.morse@....com, hanjun.guo@...aro.org,
        Sudeep Holla <sudeep.holla@....com>, dyoung@...hat.com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 1/5] arm64: export memblock_reserve()d regions via
 /proc/iomem

Hi John,

On Mon, Aug 20, 2018 at 09:39:01PM -0700, John Stultz wrote:
> On Sun, Jul 22, 2018 at 6:57 PM, AKASHI Takahiro
> <takahiro.akashi@...aro.org> wrote:
> > From: James Morse <james.morse@....com>
> >
> > There has been some confusion around what is necessary to prevent kexec
> > overwriting important memory regions. memblock: reserve, or nomap?
> > Only memblock nomap regions are reported via /proc/iomem, kexec's
> > user-space doesn't know about memblock_reserve()d regions.
> >
> > Until commit f56ab9a5b73ca ("efi/arm: Don't mark ACPI reclaim memory
> > as MEMBLOCK_NOMAP") the ACPI tables were nomap, now they are reserved
> > and thus possible for kexec to overwrite with the new kernel or initrd.
> > But this was always broken, as the UEFI memory map is also reserved
> > and not marked as nomap.
> >
> > Exporting both nomap and reserved memblock types is a nuisance as
> > they live in different memblock structures which we can't walk at
> > the same time.
> >
> > Take a second walk over memblock.reserved and add new 'reserved'
> > subnodes for the memblock_reserved() regions that aren't already
> > described by the existing code. (e.g. Kernel Code)
> >
> > We use reserve_region_with_split() to find the gaps in existing named
> > regions. This handles the gap between 'kernel code' and 'kernel data'
> > which is memblock_reserve()d, but already partially described by
> > request_standard_resources(). e.g.:
> > | 80000000-dfffffff : System RAM
> > |   80080000-80ffffff : Kernel code
> > |   81000000-8158ffff : reserved
> > |   81590000-8237efff : Kernel data
> > |   a0000000-dfffffff : Crash kernel
> > | e00f0000-f949ffff : System RAM
> >
> > reserve_region_with_split needs kzalloc() which isn't available when
> > request_standard_resources() is called, use an initcall.
> >
> > Reported-by: Bhupesh Sharma <bhsharma@...hat.com>
> > Reported-by: Tyler Baicar <tbaicar@...eaurora.org>
> > Suggested-by: Akashi Takahiro <takahiro.akashi@...aro.org>
> > Signed-off-by: James Morse <james.morse@....com>
> > Fixes: d28f6df1305a ("arm64/kexec: Add core kexec support")
> > Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > CC: Mark Rutland <mark.rutland@....com>
> > ---
> >  arch/arm64/kernel/setup.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> > index 30ad2f085d1f..5b4fac434c84 100644
> > --- a/arch/arm64/kernel/setup.c
> > +++ b/arch/arm64/kernel/setup.c
> > @@ -241,6 +241,44 @@ static void __init request_standard_resources(void)
> >         }
> >  }
> >
> > +static int __init reserve_memblock_reserved_regions(void)
> > +{
> > +       phys_addr_t start, end, roundup_end = 0;
> > +       struct resource *mem, *res;
> > +       u64 i;
> > +
> > +       for_each_reserved_mem_region(i, &start, &end) {
> > +               if (end <= roundup_end)
> > +                       continue; /* done already */
> > +
> > +               start = __pfn_to_phys(PFN_DOWN(start));
> > +               end = __pfn_to_phys(PFN_UP(end)) - 1;
> > +               roundup_end = end;
> > +
> > +               res = kzalloc(sizeof(*res), GFP_ATOMIC);
> > +               if (WARN_ON(!res))
> > +                       return -ENOMEM;
> > +               res->start = start;
> > +               res->end = end;
> > +               res->name  = "reserved";
> > +               res->flags = IORESOURCE_MEM;
> > +
> > +               mem = request_resource_conflict(&iomem_resource, res);
> > +               /*
> > +                * We expected memblock_reserve() regions to conflict with
> > +                * memory created by request_standard_resources().
> > +                */
> > +               if (WARN_ON_ONCE(!mem))
> > +                       continue;
> > +               kfree(res);
> > +
> > +               reserve_region_with_split(mem, start, end, "reserved");
> > +       }
> > +
> > +       return 0;
> > +}
> > +arch_initcall(reserve_memblock_reserved_regions);
> > +
> 
> Since this patch landed, on the HiKey board at bootup I'm seeing:
> 
> [    0.451884] WARNING: CPU: 1 PID: 1 at arch/arm64/kernel/setup.c:271
> reserve_memblock_reserved_regions+0xd4/0x13c
> [    0.451896] CPU: 1 PID: 1 Comm: swapper/0 Not tainted
> 4.18.0-10758-ga534dc3 #709
> [    0.451903] Hardware name: HiKey Development Board (DT)
> [    0.451913] pstate: 80400005 (Nzcv daif +PAN -UAO)
> [    0.451922] pc : reserve_memblock_reserved_regions+0xd4/0x13c
> [    0.451931] lr : reserve_memblock_reserved_regions+0xcc/0x13c
> [    0.451938] sp : ffffff8008053d30
> [    0.451945] x29: ffffff8008053d30 x28: ffffff8008ebe650
> [    0.451957] x27: ffffff8008ead060 x26: ffffff8008e113b0
> [    0.451969] x25: 0000000000000000 x24: 0000000000488020
> [    0.451981] x23: 0000000021ffffff x22: ffffff8008e0d860
> [    0.451993] x21: ffffff8008d74370 x20: ffffff8009019000
> [    0.452005] x19: ffffffc07507a400 x18: ffffff8009019a48
> [    0.452017] x17: 0000000000000000 x16: 0000000000000000
> [    0.452028] x15: ffffff80890e973f x14: 0000000000000006
> [    0.452040] x13: 0000000000000000 x12: 0000000000000000
> [    0.452051] x11: 0101010101010101 x10: 7f7f7f7f7f7f7f7f
> [    0.452063] x9 : 0000000000000000 x8 : ffffffc07507a480
> [    0.452074] x7 : 0000000000000000 x6 : ffffffc07ffffc30
> [    0.452086] x5 : 0000000000000000 x4 : 0000000021ffffff
> [    0.452097] x3 : 0000000000000001 x2 : 0000000000000001
> [    0.452109] x1 : 0000000000000000 x0 : 0000000000000000
> [    0.452121] Call trace:
> [    0.452130]  reserve_memblock_reserved_regions+0xd4/0x13c
> [    0.452140]  do_one_initcall+0x78/0x150
> [    0.452148]  kernel_init_freeable+0x198/0x258
> [    0.452159]  kernel_init+0x10/0x108
> [    0.452170]  ret_from_fork+0x10/0x18
> [    0.452181] ---[ end trace b4b78c443df3a750 ]---
> 
> From skimming the patch, it seems this is maybe expected? Or should
> this warning raise eyebrows? I can't quite figure it out.

Yeah, somehow.
This is the case where an inserted region has NOMAP attribute,
which means that it has no use for system memory, but is yet
"memblock_reserved." (doesn't make sense.)

> 
> It seems to trigger on the pstore memory at 0x21f00000-0x21ffffff.
> 
> /proc/iomem now has:
> ...
> 07410000-21efffff : System RAM
>   11000000-1113cfff : reserved
> 21f00000-21ffffff : reserved
>   21f00000-21f1ffff : persistent_ram
>   21f20000-21f3ffff : persistent_ram
>   21f40000-21f5ffff : persistent_ram
>   21f60000-21f7ffff : persistent_ram
>   21f80000-21f9ffff : persistent_ram
>   21fa0000-21fbffff : persistent_ram
>   21fc0000-21fdffff : persistent_ram
>   21fe0000-21ffffff : persistent_ram
> 22000000-34ffffff : System RAM
> ...

Please note that, after my patch set, there can appear a "reserved"
entry at the top level, which implies that the whole range is NOMAP'ed.

Thanks,
-Takahiro AKASHI

> 
> Where previously it had:
> ...
> 07410000-21efffff : System RAM
> 21f00000-21f1ffff : persistent_ram
> 21f20000-21f3ffff : persistent_ram
> 21f40000-21f5ffff : persistent_ram
> 21f60000-21f7ffff : persistent_ram
> 21f80000-21f9ffff : persistent_ram
> 21fa0000-21fbffff : persistent_ram
> 21fc0000-21fdffff : persistent_ram
> 21fe0000-21ffffff : persistent_ram
> 22000000-34ffffff : System RAM
> ...
> 
> 
> thanks
> -john

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