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Violators will be prosecuted for from ; Mon, 10 Jul 2017 02:00:10 -0400 Date: Sun, 9 Jul 2017 22:59:59 -0700 From: Ram Pai Subject: Re: [RFC v5 38/38] Documentation: PowerPC specific updates to memory protection keys Reply-To: Ram Pai References: <1499289735-14220-1-git-send-email-linuxram@us.ibm.com> <1499289735-14220-39-git-send-email-linuxram@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20170710055959.GD5713@ram.oc3035372033.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Anshuman Khandual 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, aneesh.kumar@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 On Mon, Jul 10, 2017 at 08:37:04AM +0530, Anshuman Khandual wrote: > On 07/06/2017 02:52 AM, Ram Pai wrote: > > Add documentation updates that capture PowerPC specific changes. > > > > Signed-off-by: Ram Pai > > --- > > Documentation/vm/protection-keys.txt | 85 ++++++++++++++++++++++++++-------- > > 1 files changed, 65 insertions(+), 20 deletions(-) > > > > diff --git a/Documentation/vm/protection-keys.txt b/Documentation/vm/protection-keys.txt > > index b643045..d50b6ab 100644 > > --- a/Documentation/vm/protection-keys.txt > > +++ b/Documentation/vm/protection-keys.txt > > @@ -1,21 +1,46 @@ > > -Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature > > -which will be found on future Intel CPUs. > > +Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature found in > > +new generation of intel CPUs and on PowerPC 7 and higher CPUs. > > > > Memory Protection Keys provides a mechanism for enforcing page-based > > -protections, but without requiring modification of the page tables > > -when an application changes protection domains. It works by > > -dedicating 4 previously ignored bits in each page table entry to a > > -"protection key", giving 16 possible keys. > > - > > -There is also a new user-accessible register (PKRU) with two separate > > -bits (Access Disable and Write Disable) for each key. Being a CPU > > -register, PKRU is inherently thread-local, potentially giving each > > -thread a different set of protections from every other thread. > > - > > -There are two new instructions (RDPKRU/WRPKRU) for reading and writing > > -to the new register. The feature is only available in 64-bit mode, > > -even though there is theoretically space in the PAE PTEs. These > > -permissions are enforced on data access only and have no effect on > > +protections, but without requiring modification of the page tables when an > > +application changes protection domains. > > + > > + > > +On Intel: > > + > > + It works by dedicating 4 previously ignored bits in each page table > > + entry to a "protection key", giving 16 possible keys. > > + > > + There is also a new user-accessible register (PKRU) with two separate > > + bits (Access Disable and Write Disable) for each key. Being a CPU > > + register, PKRU is inherently thread-local, potentially giving each > > + thread a different set of protections from every other thread. > > + > > + There are two new instructions (RDPKRU/WRPKRU) for reading and writing > > + to the new register. The feature is only available in 64-bit mode, > > + even though there is theoretically space in the PAE PTEs. These > > + permissions are enforced on data access only and have no effect on > > + instruction fetches. > > + > > + > > +On PowerPC: > > + > > + It works by dedicating 5 page table entry bits to a "protection key", > > + giving 32 possible keys. > > + > > + There is a user-accessible register (AMR) with two separate bits; > > + Access Disable and Write Disable, for each key. Being a CPU > > + register, AMR is inherently thread-local, potentially giving each > > + thread a different set of protections from every other thread. NOTE: > > + Disabling read permission does not disable write and vice-versa. > > We can only enable/disable entire access or write. Then how > read permission can be changed with protection keys directly ? Good catch. On powerpc there is a disable read and disable write. They both can be combined to disable access. Will fix the error. Read it as 'Access Read' . thanks. RP -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org