Re: set_memory_uc() does not work with pmem poison handling

[Jane Chu <jane.chu@oracle.com>]

On 6/21/2021 5:15 PM, Luis Chamberlain wrote:
> On Tue, Jun 15, 2021 at 11:55:19AM -0700, Jane Chu wrote:
>> Hi, Dan,
>>
>> It appears the fact pmem region is of WB memtype renders set_memory_uc()
>>
>> to fail due to inconsistency between the requested memtype(UC-) and the
>> cached
>>
>> memtype(WB).
>>
>> # cat /proc/iomem |grep -A 8 -i persist
>> 1840000000-d53fffffff : Persistent Memory
>>    1840000000-1c3fffffff : namespace0.0
>>    5740000000-76bfffffff : namespace2.0
>>
>> # cat /sys/kernel/debug/x86/pat_memtype_list
>> PAT memtype list:
>> PAT: [mem 0x0000001840000000-0x0000001c40000000] write-back
>> PAT: [mem 0x0000005740000000-0x00000076c0000000] write-back
>>
>> [10683.418072] Memory failure: 0x1850600: recovery action for dax page:
>> Recovered
>> [10683.426147] x86/PAT: fsdax_poison_v1:5018 conflicting memory types
>> 1850600000-1850601000  uncached-minus<->write-back
>>
>> cscope search shows that unlike pmem, set_memory_uc() is primarily used by
>> drivers dealing with ioremap(),
> 
> Yes, when a driver *knows* the type must follow certain rules, it
> requests it.
> 
>> perhaps the pmem case needs another way to suppress prefetch?
>>
>> Your thoughts?
> 
> The way to think about this problem is, who did the ioremap call for the
> ioremap'd area? That's the driver that needs changing.

I'm not sure if the pmem driver is doing something wrong, but rather the
pmem memory failure handler.

thanks,
-jane

> 
>    Luis
>