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 <linuxram@xxxxxxxxxx> > > --- > > 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
