[PATCH] [PATCH] arm64: Boot failure on m400 with new cont PTEs
jeremy.linton at arm.com
Wed Nov 18 08:08:58 PST 2015
On 11/18/2015 09:20 AM, Mark Rutland wrote:
> Hi Jeremy,
> On Wed, Nov 18, 2015 at 09:03:19AM -0600, Jeremy Linton wrote:
>> The HP m400 fails to boot the linux 4.4rc1 kernel.
> Are you using defconfig? If not, can you share your config?
No, its not defconfig, its roughly the RHELSA config tossed into a
mainline 4.4 tree and all the default options selected. AFAIK RHELSA is
still limited access.
>> It usually hangs or sometimes takes an unhanded exception around the
>> DMA zone messages. This was bisected to the new CONT PTE changes.
> Do you have any examples of the unhandled exception cases? Are they a
> mixed bag, or a consistent exception class?
I'm guessing about 90% of the time its a dead hang, the remaining are
the faults of which there is one that happens more frequently than the
others. Here is one i found in my notes..
[ 0.000000] On node 0 totalpages: 1048512
[ 0.000000] DMA zone: 64 pages used for memmap
[ 0.000000] DMA zone: 0 pages reserved
[ 0.000000] DMA zone: 65472 pages, LIFO batch:1
[ 0.000000] Unhandled fault: unknown 48 (0x96000070) at
>> Adding an extra flush_tlb_all() in the code path which is
>> changing the kernel permissions allows the machine to boot
> As you mention changing permissions, I take it you're using
The failing configuration doesn't have DEBUG_RODATA set, I might have
been pretty loose with my terminology.
Frankly, I wondered originally how config RODATA was working reliably
because the flushes were only around the directories getting split,
fixup_init() (and basically anything calling create_mapping_late())
looked like there were paths that could avoid flushing. When I added the
CONT changes I didn't add flushes to paths that didn't previously have
them (except in the split cont range case, which matched the spit p[mu]d
case). I made the mistake of assuming someone knew about some edge case
that avoided the need for the flush.
Once I find/fix the console issue on that machine with 4.4rc1 (there are
a small handful of issues that keep mainline from working on it,
including the sata patch that was posted, and rejected), I will focus on
hoisting the tlb flush into create_mapping_late() and removing the
splattering of flushes in those code paths. That is unless there is a
reason to be preforming them as soon as the directories are split.
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