linux-kernel - Re: [RFC v5 00/38] powerpc: Memory Protection Keys

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Date:   Sun, 9 Jul 2017 23:05:44 -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 00/38] powerpc: Memory Protection Keys

On Mon, Jul 10, 2017 at 11:13:23AM +0530, Anshuman Khandual wrote:
> On 07/06/2017 02:51 AM, Ram Pai wrote:
> > Memory protection keys enable applications to protect its
> > address space from inadvertent access or corruption from
> > itself.
> > 
> > The overall idea:
> > 
> >  A process allocates a   key  and associates it with
> >  an  address  range  within    its   address   space.
> >  The process  then  can  dynamically  set read/write 
> >  permissions on  the   key   without  involving  the 
> >  kernel. Any  code that  violates   the  permissions
> >  of  the address space; as defined by its associated
> >  key, will receive a segmentation fault.
> > 
> > This patch series enables the feature on PPC64 HPTE
> > platform.
> > 
> > ISA3.0 section 5.7.13 describes the detailed specifications.
> > 
> > 
> > Testing:
> > 	This patch series has passed all the protection key
> > 	tests available in  the selftests directory.
> > 	The tests are updated to work on both x86 and powerpc.
> > 
> > version v5:
> > 	(1) reverted back to the old design -- store the 
> > 	    key in the pte, instead of bypassing it.
> > 	    The v4 design slowed down the hash page path.
> > 	(2) detects key violation when kernel is told to 
> > 		access user pages.
> > 	(3) further refined the patches into smaller consumable
> > 		units
> > 	(4) page faults handlers captures the faulting key 
> > 	    from the pte instead of the vma. This closes a
> > 	    race between where the key update in the vma and
> > 	    a key fault caused cause by the key programmed
> > 	    in the pte.
> > 	(5) a key created with access-denied should
> > 	    also set it up to deny write. Fixed it.
> > 	(6) protection-key number is displayed in smaps
> > 		the x86 way.
> 
> Hello Ram,
> 
> This patch series has now grown a lot. Do you have this
> hosted some where for us to pull and test it out ? BTW

https://github.com/rampai/memorykeys.git
branch memkey.v5.3

> do you have data points to show the difference in
> performance between this version and the last one where
> we skipped the bits from PTE and directly programmed the
> HPTE entries looking into VMA bits.

No. I dont. I am hoping you can help me out with this.
RP