Re: [PATCH] powerpc/lpar: Don't crash on H_PROTECT errors

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

On 02/29/2016 10:20 PM, Tyrel Datwyler wrote:
> On 02/29/2016 03:52 AM, Anshuman Khandual wrote:
>> There are certain condition in which H_PROTECT can return error code
>> other than H_NOT_FOUND and H_SUCCESS. One such being an attempt to
>> update an hpte owned by adjunct partition. Return 0 in that case so
>> that user space will retry the access. In adjunct case this mean we
>> will not make much progress in the user space. But atleast we get a
>> chance to kill the task and avoid taking down the entire box.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
>> ---
>>  arch/powerpc/platforms/pseries/lpar.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
>> index 477290a..31bcdaf 100644
>> --- a/arch/powerpc/platforms/pseries/lpar.c
>> +++ b/arch/powerpc/platforms/pseries/lpar.c
>> @@ -310,7 +310,7 @@ static long pSeries_lpar_hpte_updatepp(unsigned long slot,
>>  
>>  	pr_devel("ok\n");
>>  
>> -	BUG_ON(lpar_rc != H_SUCCESS);
>> +	WARN_RATELIMIT(lpar_rc != H_SUCCESS, "H_PROTECT returned %lu\n", lpar_rc);
> 
> In the event that we don't get H_NOT_FOUND (which is handled earlier in
> the function) or H_SUCCESS this patch assumes H_RESOURCE. It fails to
> handle H_PARAMETER which is also a valid return from the H_PROTECT
> hypercall.

Right, I guess its okay to BUG_ON() if we detect H_PARAMETER return code
as the kernel should not have created wrong arguments to the hcall in
the first place. Although we will still want to return 0 from here for
H_RESOURCE return code with a WARN_RATELIMIT message. Will change the
code accordingly next time around.