linux-kernel - Re: [PATCH] of/fdt: Make sure no-map does not remove already reserved regions

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Date:   Tue, 16 Jul 2019 17:12:01 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        Nicolas Boichat <drinkcat@...omium.org>
Cc:     Frank Rowand <frowand.list@...il.com>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ian Campbell <ian.campbell@...rix.com>,
        Grant Likely <grant.likely@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH] of/fdt: Make sure no-map does not remove already reserved regions

On Tue, Jul 16, 2019 at 4:46 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>
> On 7/2/19 10:08 PM, Nicolas Boichat wrote:
> > If the device tree is incorrectly configured, and attempts to
> > define a "no-map" reserved memory that overlaps with the kernel
> > data/code, the kernel would crash quickly after boot, with no
> > obvious clue about the nature of the issue.
> >
> > For example, this would happen if we have the kernel mapped at
> > these addresses (from /proc/iomem):
> > 40000000-41ffffff : System RAM
> >   40080000-40dfffff : Kernel code
> >   40e00000-411fffff : reserved
> >   41200000-413e0fff : Kernel data
> >
> > And we declare a no-map shared-dma-pool region at a fixed address
> > within that range:
> > mem_reserved: mem_region {
> >       compatible = "shared-dma-pool";
> >       reg = <0 0x40000000 0 0x01A00000>;
> >       no-map;
> > };
> >
> > To fix this, when removing memory regions at early boot (which is
> > what "no-map" regions do), we need to make sure that the memory
> > is not already reserved. If we do, __reserved_mem_reserve_reg
> > will throw an error:
> > [    0.000000] OF: fdt: Reserved memory: failed to reserve memory
> >    for node 'mem_region': base 0x0000000040000000, size 26 MiB
> > and the code that will try to use the region should also fail,
> > later on.
> >
> > We do not do anything for non-"no-map" regions, as memblock
> > explicitly allows reserved regions to overlap, and the commit
> > that this fixes removed the check for that precise reason.
> >
> > Fixes: 094cb98179f19b7 ("of/fdt: memblock_reserve /memreserve/ regions in the case of partial overlap")
> > Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> > ---
> >  drivers/of/fdt.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > index cd17dc62a71980a..a1ded43fc332d0c 100644
> > --- a/drivers/of/fdt.c
> > +++ b/drivers/of/fdt.c
> > @@ -1138,8 +1138,16 @@ int __init __weak early_init_dt_mark_hotplug_memory_arch(u64 base, u64 size)
> >  int __init __weak early_init_dt_reserve_memory_arch(phys_addr_t base,
> >                                       phys_addr_t size, bool nomap)
> >  {
> > -     if (nomap)
> > +     if (nomap) {
> > +             /*
> > +              * If the memory is already reserved (by another region), we
> > +              * should not allow it to be removed altogether.
> > +              */
> > +             if (memblock_is_region_reserved(base, size))
> > +                     return -EBUSY;
> > +
> >               return memblock_remove(base, size);
>
> While you are it, the nomap argument (introduced with
> e8d9d1f5485b52ec3c4d7af839e6914438f6c285) predates the introduction of
> memblock_is_nomap() (bf3d3cc580f9960883ebf9ea05868f336d9491c2), so
> should just remove memblock_remove() and use memblock_mark_nomap()
> instead here.

Perhaps like this patch[1]? Though the reasoning is different and the
commit message here is more thorough, so can I get a combined patch.
However, I don't under how handling a misconfigured DT and aligned
with EFI are the same patch. What's considered valid for EFI is not
for DT regions?

Rob

[1] https://patchwork.ozlabs.org/patch/1131232/