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Subject: Re: [PATCH] of/fdt: Make sure no-map does not remove already reserved
 regions
To:     Rob Herring <robh+dt@kernel.org>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        Nicolas Boichat <drinkcat@chromium.org>
Cc:     Frank Rowand <frowand.list@gmail.com>, devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ian Campbell <ian.campbell@citrix.com>,
        Grant Likely <grant.likely@linaro.org>,
        Stephen Boyd <swboyd@chromium.org>
References: <20190703050827.173284-1-drinkcat@chromium.org>
 <815a8414-bfbe-c693-3208-1580779815ec@gmail.com>
 <CAL_JsqLETdazfnz5EU0Qw4TVVBhWmzk12Z5zYMo5Hm2ACPXh1w@mail.gmail.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
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Date:   Tue, 16 Jul 2019 16:17:10 -0700
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On 7/16/19 4:12 PM, Rob Herring wrote:
> On Tue, Jul 16, 2019 at 4:46 PM Florian Fainelli <f.fainelli@gmail.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@chromium.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.

From a quick reading it does look like memblock_isolate_range(), as
called by memblock_setclr_flag() should be able to detect this region
was already reserved, though I have not tried it.

> 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?

That I don't know how to answer.
-- 
Florian