Subject: Re: [PATCH -V5 13/25] powerpc: Update tlbie/tlbiel as per ISA doc

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 11 Apr 2013 10:50:12 +0530

David Gibson <[email-masked]> writes:

> On Thu, Apr 04, 2013 at 11:27:51AM +0530, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <[email-masked]>
>> 
>> This make sure we handle multiple page size segment correctly.
>
> This needs a much more detailed message.  In what way was the existing
> code not matching the ISA documentation?  What consequences did that
> have?

Mostly to make sure we use the right penc values in tlbie. I did test
these changes on PowerNV. 

>
>> 
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> ---
>>  arch/powerpc/mm/hash_native_64.c |   30 ++++++++++++++++++++++++++++--
>>  1 file changed, 28 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/powerpc/mm/hash_native_64.c b/arch/powerpc/mm/hash_native_64.c
>> index b461b2d..ac84fa6 100644
>> --- a/arch/powerpc/mm/hash_native_64.c
>> +++ b/arch/powerpc/mm/hash_native_64.c
>> @@ -61,7 +61,10 @@ static inline void __tlbie(unsigned long vpn, int psize, int apsize, int ssize)
>>  
>>  	switch (psize) {
>>  	case MMU_PAGE_4K:
>> +		/* clear out bits after (52) [0....52.....63] */
>> +		va &= ~((1ul << (64 - 52)) - 1);
>>  		va |= ssize << 8;
>> +		va |= mmu_psize_defs[apsize].sllp << 6;
>
> sllp is the per-segment encoding, so it sure must be looked up via
> psize, not apsize.

as per ISA doc, for base page size 4K, RB[56:58] must be set to
SLB[L|LP] encoded for the page size corresponding to the actual page
size specified by the PTE that was used to create the the TLB entry to
be invalidated.

>
>>  		asm volatile(ASM_FTR_IFCLR("tlbie %0,0", PPC_TLBIE(%1,%0), %2)
>>  			     : : "r" (va), "r"(0), "i" (CPU_FTR_ARCH_206)
>>  			     : "memory");
>> @@ -69,9 +72,19 @@ static inline void __tlbie(unsigned long vpn, int psize, int apsize, int ssize)
>>  	default:
>>  		/* We need 14 to 14 + i bits of va */
>>  		penc = mmu_psize_defs[psize].penc[apsize];
>> -		va &= ~((1ul << mmu_psize_defs[psize].shift) - 1);
>> +		va &= ~((1ul << mmu_psize_defs[apsize].shift) - 1);
>>  		va |= penc << 12;
>>  		va |= ssize << 8;
>> +		/* Add AVAL part */
>> +		if (psize != apsize) {
>> +			/*
>> +			 * MPSS, 64K base page size and 16MB parge page size
>> +			 * We don't need all the bits, but this seems to work.
>> +			 * vpn cover upto 65 bits of va. (0...65) and we need
>> +			 * 58..64 bits of va.
>
> "seems to work" is not a comment I like to see in core MMU code...
>

As per ISA spec, the "other bits" in RB[56:62] must be ignored by the
processor. Hence I didn't bother to do zero it out. Since we only
support one MPSS combination, we could easily zero out using 0xf0. 

-aneesh