linux-kernel - Re: [RFC v2 00/12] powerpc: Memory Protection Keys

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Date:   Tue, 20 Jun 2017 15:10:15 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        dave.hansen@...el.com, hbabu@...ibm.com
Subject: Re: [RFC v2 00/12] powerpc: Memory Protection Keys

On Fri, 2017-06-16 at 20:52 -0700, Ram Pai wrote:
> Memory protection keys enable applications to protect its
> address space from inadvertent access or corruption from
> itself.

I presume by itself you mean protection between threads?

> 
> The overall idea:
> 
>  A process allocates a   key  and associates it with
>  a  address  range  within    its   address   space.

OK, so this is per VMA?

>  The process  than  can  dynamically  set read/write 
>  permissions on  the   key   without  involving  the 
>  kernel.

This bit is not clear, how can the key be set without
involving the kernel? I presume you mean the key is set
in the PTE's and the access protection values can be
set without involving the kernel?

 Any  code that  violates   the  permissions
>  off the address space; as defined by its associated
>  key, will receive a segmentation fault.
> 
> This patch series enables the feature on PPC64.
> It is enabled on HPTE 64K-page 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.

Balbir