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

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Message-Id: <20170710055502.GC5713@ram.oc3035372033.ibm.com>
Date:   Sun, 9 Jul 2017 22:55:02 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     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 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?
RP

-- 
Ram Pai