Date: Wed, 28 Jun 2017 00:12:28 -0700
From: Ram Pai <linuxram@us.ibm.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
        khandual@linux.vnet.ibm.com, bsingharora@gmail.com,
        dave.hansen@intel.com, hbabu@us.ibm.com, arnd@arndb.de,
        akpm@linux-foundation.org, corbet@lwn.net, mingo@redhat.com
Subject: Re: [RFC v4 09/17] powerpc: call the hash functions with the correct
 pkey value
Reply-To: Ram Pai <linuxram@us.ibm.com>
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On Tue, Jun 27, 2017 at 08:54:07PM +0530, Aneesh Kumar K.V wrote:
> 
> 
> On Tuesday 27 June 2017 03:41 PM, Ram Pai wrote:
> >Pass the correct protection key value to the hash functions on
> >page fault.
> >
> >Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> >---
> >  arch/powerpc/include/asm/pkeys.h | 11 +++++++++++
> >  arch/powerpc/mm/hash_utils_64.c  |  4 ++++
> >  arch/powerpc/mm/mem.c            |  6 ++++++
> >  3 files changed, 21 insertions(+)
> >
> >diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> >index ef1c601..1370b3f 100644
> >--- a/arch/powerpc/include/asm/pkeys.h
> >+++ b/arch/powerpc/include/asm/pkeys.h
> >@@ -74,6 +74,17 @@ static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
> >  }
> >
> >  /*
> >+ * return the protection key of the vma corresponding to the
> >+ * given effective address @ea.
> >+ */
> >+static inline int mm_pkey(struct mm_struct *mm, unsigned long ea)
> >+{
> >+	struct vm_area_struct *vma = find_vma(mm, ea);
> >+	int pkey = vma ? vma_pkey(vma) : 0;
> >+	return pkey;
> >+}
> >+
> >+/*
> >
> 
> That is not going to work in hash fault path right ? We can't do a
> find_vma there without holding the mmap_sem

There is a fundamental problem with this new design. Looks like we can't
hold a lock in that path, without badly hurting the performance.

I am moving back to the old design. Cant by-pass the pte. The
keys will be programmed into the pte which will than be used
to program the hpte.

RP