On Wed, Nov 26, 2014 at 1:14 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Tue, 2014-11-25 at 13:31 -0600, Rob Herring wrote:
>> On Tue, Nov 25, 2014 at 8:37 AM, Grant Likely <grant.likely@xxxxxxxxxx> wrote:
>> > On Tue, 25 Nov 2014 12:54:55 +0000
>> > , Ian Campbell <ian.campbell@xxxxxxxxxx>
>> > wrote:
>> >> memblock_is_region_reserved() returns true in the case of a partial
>> >> overlap, meaning that the current code fails to reserve the
>> >> non-overlapping portion.
>> >>
>> >> I observed this causing a Midway system with a buggy fdt (the header
>> >> declares itself to be larger than it really is) failing to boot
>> >> because the over-inflated size of the fdt was causing it to seem to
>> >> run into the swapper_pg_dir region, meaning the DT wasn't reserved.
>> >> The symptoms were failing to find an disks or network and failing to
>> >> boot. I think it is work printing a warning in this case.
>> >>
>> >> However given the ambiguity of whether things like the initrd are
>> >> covered by /memreserve/ and similar I think it is best to also
>> >> register the region rather than just ignoring it.
>> >>
>> >> Since memblock_reserve() handles overlaps just fine lets just warn and
>> >> carry on.
>> >>
>> >> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>> >> Cc: Grant Likely <grant.likely@xxxxxxxxxx>
>> >> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
>> >> Cc: devicetree@xxxxxxxxxxxxxxx
>> >> ---
>> >> drivers/of/fdt.c | 3 ++-
>> >> 1 file changed, 2 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>> >> index 30e97bc..4f0f24c 100644
>> >> --- a/drivers/of/fdt.c
>> >> +++ b/drivers/of/fdt.c
>> >> @@ -965,7 +965,8 @@ int __init __weak early_init_dt_reserve_memory_arch(phys_addr_t base,
>> >> phys_addr_t size, bool nomap)
>> >> {
>> >> if (memblock_is_region_reserved(base, size))
>> >> - return -EBUSY;
>> >> + pr_warning("DT reserved region at 0x%pa is already reserved\n",
>> >> + &base);
>> >
>> > Since memblock_remove/reserve does the right thing anyway, let's just
>> > drop the test entirely.
>>
>> If the region completely overlaps, then I agree it is okay to be
>> quiet. But if we have partially overlapping region already with the
>> dtb, then we should warn here. We want to know if someone passes a dtb
>> that is too big.
>
> Unfortunately memblock isn't currently capable of distinguishing partial
> vs total overlap.
>
> We could perhaps warn iff only on of the first and last byte of the new
> region are already reserved, but not if they both are. i.e.
> if (memblock_is_region_reserved(base, size) &&
> !!memblock_is_region_reserved(base, 1) != !!memblock_is_region_reserved(base+size-1, 1))
>
> That wouldn't handle
> ----RESERVED---| |----RESERVED-----
> |----- NEW REGION----|
>
> But maybe it's better than nothing.
>
> Or we could pull the warning up to the caller which reserves the DTB but
> not for the /memreserve/ loop.
I've merged the patch to always reserve the region since it is safe.
I'll expect a followup patch to print a warning in the partial overlap
case.
g.
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
