Re: [PATCH] powerpc: Fix bad pmd error with book3E config

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Michael Neuling <mikey@neuling.org> writes:

> Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> wrote:
>
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>> 
>> Book3E uses the hugepd at PMD level and don't encode pte directly
>> at the pmd level. So it will find the lower bits of pmd set
>> and the pmd_bad check throws error. Infact the current code
>> will never take the free_hugepd_range call at all because it will
>> clear the pmd if it find a hugepd pointer.
>> 
>
> Please explain what changes you are making.  Currently you are only
> describing what the issue is.

will do

>
> Also include which the SHA1 which caused the regression (ie
> e2b3d202d1dba8f3546ed28224ce485bc50010be "powerpc: Switch 16GB and 16MB
> explicit hugepages to a different page table format")

will add

>
> Mikey
>
>> Reported-by: Scott Wood <scottwood@freescale.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> ---
>>  arch/powerpc/mm/hugetlbpage.c | 29 ++++++++++++++++++-----------
>>  1 file changed, 18 insertions(+), 11 deletions(-)
>> 
>> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
>> index f2f01fd..0d3d3ee 100644
>> --- a/arch/powerpc/mm/hugetlbpage.c
>> +++ b/arch/powerpc/mm/hugetlbpage.c
>> @@ -536,19 +536,26 @@ static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
>>  	do {
>>  		pmd = pmd_offset(pud, addr);
>>  		next = pmd_addr_end(addr, end);
>> -		if (pmd_none_or_clear_bad(pmd))
>> -			continue;
>> +		if (!is_hugepd(pmd)) {
>> +			/*
>> +			 * if it is not hugepd pointer, we should already find
>> +			 * it cleared.
>> +			 */
>> +			if (!pmd_none_or_clear_bad(pmd))
>> +				WARN_ON(1);
>
> How often are we going to hit this?    Should this be a warn_on once or
> even a bug_on?

it should never happen. But i was thinking killing the system may a bit
too much, hence WARN_ON

>
> Also just make it: 
>   WARN_ON(!pmd_none_or_clear_bad(pmd))
>

will do

-aneesh