linux-kernel - Re: [RFC v5 31/38] powerpc: introduce get_pte

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Date:   Tue, 11 Jul 2017 16:52:40 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Ram Pai <linuxram@...ibm.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        aneesh.kumar@...ux.vnet.ibm.com, bsingharora@...il.com,
        dave.hansen@...el.com, hbabu@...ibm.com, arnd@...db.de,
        akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v5 31/38] powerpc: introduce get_pte_pkey() helper

On 07/10/2017 11:25 AM, Ram Pai wrote:
> On Mon, Jul 10, 2017 at 08:41:30AM +0530, Anshuman Khandual wrote:
>> On 07/06/2017 02:52 AM, Ram Pai wrote:
>>> get_pte_pkey() helper returns the pkey associated with
>>> a address corresponding to a given mm_struct.
>>>
>>> Signed-off-by: Ram Pai <linuxram@...ibm.com>
>>> ---
>>>  arch/powerpc/include/asm/book3s/64/mmu-hash.h |    5 ++++
>>>  arch/powerpc/mm/hash_utils_64.c               |   28 +++++++++++++++++++++++++
>>>  2 files changed, 33 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/book3s/64/mmu-hash.h b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
>>> index f7a6ed3..369f9ff 100644
>>> --- a/arch/powerpc/include/asm/book3s/64/mmu-hash.h
>>> +++ b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
>>> @@ -450,6 +450,11 @@ extern int hash_page(unsigned long ea, unsigned long access, unsigned long trap,
>>>  int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
>>>  		     pte_t *ptep, unsigned long trap, unsigned long flags,
>>>  		     int ssize, unsigned int shift, unsigned int mmu_psize);
>>> +
>>> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>>> +u16 get_pte_pkey(struct mm_struct *mm, unsigned long address);
>>> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>>> +
>>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>  extern int __hash_page_thp(unsigned long ea, unsigned long access,
>>>  			   unsigned long vsid, pmd_t *pmdp, unsigned long trap,
>>> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
>>> index 1e74529..591990c 100644
>>> --- a/arch/powerpc/mm/hash_utils_64.c
>>> +++ b/arch/powerpc/mm/hash_utils_64.c
>>> @@ -1573,6 +1573,34 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
>>>  	local_irq_restore(flags);
>>>  }
>>>  
>>> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>>> +/*
>>> + * return the protection key associated with the given address
>>> + * and the mm_struct.
>>> + */
>>> +u16 get_pte_pkey(struct mm_struct *mm, unsigned long address)
>>> +{
>>> +	pte_t *ptep;
>>> +	u16 pkey = 0;
>>> +	unsigned long flags;
>>> +
>>> +	if (REGION_ID(address) == VMALLOC_REGION_ID)
>>> +		mm = &init_mm;
>>
>> IIUC, protection keys are only applicable for user space. This
>> function is getting used to populate siginfo structure. Then how
>> can we ever request this for any address in VMALLOC region.
> 
> make sense. this check is not needed.
> 
>>
>>> +
>>> +	if (!mm || !mm->pgd)
>>> +		return 0;
>>
>> Is this really required at this stage ?
> 
> its a sanity check to gaurd against bad inputs. See a problem?


I mean its okay, thought it to be unnecessary. Your call.