[PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Reza Arbab]

In htab_convert_pte_flags(), _PAGE_CACHE_CTL is used to check for the
_PAGE_SAO flag:

  else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
          rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);

But, it isn't defined to include that flag:

  #define _PAGE_CACHE_CTL (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)

This happens to work, but only because of the flag values:

  #define _PAGE_SAO               0x00010 /* Strong access order */
  #define _PAGE_NON_IDEMPOTENT    0x00020 /* non idempotent memory */
  #define _PAGE_TOLERANT          0x00030 /* tolerant memory, cache inhibited */

To prevent any issues if these particulars ever change, add _PAGE_SAO to
the mask.

Suggested-by: Charles Johns <crjohns@us.ibm.com>
Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 2e6ada2..1d97a28 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -811,7 +811,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
 	return hash__set_pte_at(mm, addr, ptep, pte, percpu);
 }
 
-#define _PAGE_CACHE_CTL	(_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
+#define _PAGE_CACHE_CTL	(_PAGE_SAO | _PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
 
 #define pgprot_noncached pgprot_noncached
 static inline pgprot_t pgprot_noncached(pgprot_t prot)
-- 
1.8.3.1

Re: [PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Alexey Kardashevskiy]

On 29/01/2019 04:31, Reza Arbab wrote:
> In htab_convert_pte_flags(), _PAGE_CACHE_CTL is used to check for the
> _PAGE_SAO flag:
> 
>   else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>           rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
> 
> But, it isn't defined to include that flag:
> 
>   #define _PAGE_CACHE_CTL (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> 
> This happens to work, but only because of the flag values:
> 
>   #define _PAGE_SAO               0x00010 /* Strong access order */
>   #define _PAGE_NON_IDEMPOTENT    0x00020 /* non idempotent memory */
>   #define _PAGE_TOLERANT          0x00030 /* tolerant memory, cache inhibited */
> 
> To prevent any issues if these particulars ever change, add _PAGE_SAO to
> the mask.


This does not feel right, doing

#define _PAGE_CACHE_CTL	0x30

would make more sense as SAO/NI/TOLERANT is enum so applying "|" to them
just seems wrong.


> 
> Suggested-by: Charles Johns <crjohns@us.ibm.com>
> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
> ---
>  arch/powerpc/include/asm/book3s/64/pgtable.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 2e6ada2..1d97a28 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -811,7 +811,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
>  	return hash__set_pte_at(mm, addr, ptep, pte, percpu);
>  }
>  
> -#define _PAGE_CACHE_CTL	(_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> +#define _PAGE_CACHE_CTL	(_PAGE_SAO | _PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
>  
>  #define pgprot_noncached pgprot_noncached
>  static inline pgprot_t pgprot_noncached(pgprot_t prot)
> 

-- 
Alexey

Re: [PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Aneesh Kumar K.V]

On 1/28/19 11:01 PM, Reza Arbab wrote:
> In htab_convert_pte_flags(), _PAGE_CACHE_CTL is used to check for the
> _PAGE_SAO flag:
> 
>    else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>            rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
> 
> But, it isn't defined to include that flag:
> 
>    #define _PAGE_CACHE_CTL (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> 
> This happens to work, but only because of the flag values:
> 
>    #define _PAGE_SAO               0x00010 /* Strong access order */
>    #define _PAGE_NON_IDEMPOTENT    0x00020 /* non idempotent memory */
>    #define _PAGE_TOLERANT          0x00030 /* tolerant memory, cache inhibited */
> 
> To prevent any issues if these particulars ever change, add _PAGE_SAO to
> the mask.
> 

Not sure what the fix is about. We set the related hash pte flags via

	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_TOLERANT)
		rflags |= HPTE_R_I;
	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_NON_IDEMPOTENT)
		rflags |= (HPTE_R_I | HPTE_R_G);
	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
		rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
	else
		/*
		 * Add memory coherence if cache inhibited is not set
		 */
		rflags |= HPTE_R_M;




> Suggested-by: Charles Johns <crjohns@us.ibm.com>
> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
> ---
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 2e6ada2..1d97a28 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -811,7 +811,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
>   	return hash__set_pte_at(mm, addr, ptep, pte, percpu);
>   }
>   
> -#define _PAGE_CACHE_CTL	(_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> +#define _PAGE_CACHE_CTL	(_PAGE_SAO | _PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
>   
>   #define pgprot_noncached pgprot_noncached
>   static inline pgprot_t pgprot_noncached(pgprot_t prot)
> 

Re: [PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Reza Arbab]

On Tue, Jan 29, 2019 at 08:37:28PM +0530, Aneesh Kumar K.V wrote:
>Not sure what the fix is about. We set the related hash pte flags via
>
>	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_TOLERANT)
>		rflags |= HPTE_R_I;
>	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_NON_IDEMPOTENT)
>		rflags |= (HPTE_R_I | HPTE_R_G);
>	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>		rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);

Again, nothing broken here, just a code readability thing. As Alexey 
(and Charlie) noted, given the above it is a little confusing to define 
_PAGE_CACHE_CTL this way:

  #define _PAGE_CACHE_CTL      (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)

I like Alexey's idea, maybe just use a literal?

  #define _PAGE_CACHE_CTL 0x30

-- 
Reza Arbab

Re: [PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Michael Ellerman]

Reza Arbab <arbab@linux.ibm.com> writes:

> On Tue, Jan 29, 2019 at 08:37:28PM +0530, Aneesh Kumar K.V wrote:
>>Not sure what the fix is about. We set the related hash pte flags via
>>
>>	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_TOLERANT)
>>		rflags |= HPTE_R_I;
>>	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_NON_IDEMPOTENT)
>>		rflags |= (HPTE_R_I | HPTE_R_G);
>>	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>>		rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
>
> Again, nothing broken here, just a code readability thing. As Alexey 
> (and Charlie) noted, given the above it is a little confusing to define 
> _PAGE_CACHE_CTL this way:
>
>   #define _PAGE_CACHE_CTL      (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)

Yeah that's confusing I agree.

It's not really a maintainability thing, because those bits are in the
architecture, so they can't change.

> I like Alexey's idea, maybe just use a literal?
>
>   #define _PAGE_CACHE_CTL 0x30

I prefer your original patch. It serves as documentation on what values
we expect to see in that field.

cheers

Re: [PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Alexey Kardashevskiy]

On 31/01/2019 00:35, Michael Ellerman wrote:
> Reza Arbab <arbab@linux.ibm.com> writes:
> 
>> On Tue, Jan 29, 2019 at 08:37:28PM +0530, Aneesh Kumar K.V wrote:
>>> Not sure what the fix is about. We set the related hash pte flags via
>>>
>>> 	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_TOLERANT)
>>> 		rflags |= HPTE_R_I;
>>> 	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_NON_IDEMPOTENT)
>>> 		rflags |= (HPTE_R_I | HPTE_R_G);
>>> 	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>>> 		rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
>>
>> Again, nothing broken here, just a code readability thing. As Alexey 
>> (and Charlie) noted, given the above it is a little confusing to define 
>> _PAGE_CACHE_CTL this way:
>>
>>   #define _PAGE_CACHE_CTL      (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> 
> Yeah that's confusing I agree.
> 
> It's not really a maintainability thing, because those bits are in the
> architecture, so they can't change.
> 
>> I like Alexey's idea, maybe just use a literal?
>>
>>   #define _PAGE_CACHE_CTL 0x30
> 
> I prefer your original patch. It serves as documentation on what values
> we expect to see in that field.


As documentation, it gives an idea that there can be both
_PAGE_NON_IDEMPOTENT and _PAGE_TOLERANT set which is not true. Putting
possible values in the comment next to "#define _PAGE_CACHE_CTL" will
document it properly imho.



-- 
Alexey

Re: powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask

[Michael Ellerman]

On Mon, 2019-01-28 at 17:31:42 UTC, Reza Arbab wrote:
> In htab_convert_pte_flags(), _PAGE_CACHE_CTL is used to check for the
> _PAGE_SAO flag:
> 
>   else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>           rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
> 
> But, it isn't defined to include that flag:
> 
>   #define _PAGE_CACHE_CTL (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> 
> This happens to work, but only because of the flag values:
> 
>   #define _PAGE_SAO               0x00010 /* Strong access order */
>   #define _PAGE_NON_IDEMPOTENT    0x00020 /* non idempotent memory */
>   #define _PAGE_TOLERANT          0x00030 /* tolerant memory, cache inhibited */
> 
> To prevent any issues if these particulars ever change, add _PAGE_SAO to
> the mask.
> 
> Suggested-by: Charles Johns <crjohns@us.ibm.com>
> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/865a9432d16fe2f40a1a52005fd30778

cheers