[Skiboot-stable] [PATCH] phb4/5: Escalate page-level TCE kills

[Frederic Barrat]

On 26/08/2021 17:47, Oliver O'Halloran wrote:
> On Thu, Aug 26, 2021 at 1:09 AM Frederic Barrat <fbarrat at linux.ibm.com> wrote:
>>
>> An hw issue was found on P10 (HW560152) where a page-level TCE kill
>> can be dropped if there are enough TCE kill requests already being
>> processed. The net effect is that data integrity is not
>> guaranteed.
> 
> Hmm, what is the actual problem? Is there a race between when the bit
> in TCE_KILL says there's a free queue slot and when one actually comes
> available? If so, how big is that race window?

Not quite. We need to have the queue backed up with a mix of PE-level 
and page-level kills. And if there's the right sequence of those in the 
queue, then a page level kill is dropped.

   Fred


>> The circumvention is to stay away from page-level kills
>> and escalate those to PE kills. Which hurts performance.
> 
> understatement
> 
>> It also affects P9.
> 
> lol
> 
> 
>>
>> Signed-off-by: Frederic Barrat <fbarrat at linux.ibm.com>
>> ---
>>   hw/phb4.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/hw/phb4.c b/hw/phb4.c
>> index 79083d4a..ddaa18f8 100644
>> --- a/hw/phb4.c
>> +++ b/hw/phb4.c
>> @@ -1051,6 +1051,14 @@ static int64_t phb4_tce_kill(struct phb *phb, uint32_t kill_type,
>>          uint64_t val;
>>          int64_t rc;
>>
>> +       /*
>> +        * HW560152: a page-level kill can be dropped if the
>> +        *       processing queue is backed-up, which can cause data
>> +        *       integrity issues
>> +        */
>> +       if (kill_type == OPAL_PCI_TCE_KILL_PAGES)
>> +               kill_type = OPAL_PCI_TCE_KILL_PE;
>> +
>>          sync();
>>          switch(kill_type) {
>>          case OPAL_PCI_TCE_KILL_PAGES:
>> --
>> 2.31.1
>>
>> --
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