Messages in this thread | | | Date | Mon, 26 Mar 2018 18:03:53 -0700 | From | Ram Pai <> | Subject | Re: [PATCH] powerpc, pkey: make protection key 0 less special |
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On Mon, Mar 26, 2018 at 04:31:41PM -0700, Ram Pai wrote: > Applications need the ability to associate an address-range with some > key and latter revert to its initial default key. Pkey-0 comes close to > providing this function but falls short, because the current > implementation disallows applications to explicitly associate pkey-0 to > the address range. > > Lets make pkey-0 less special and treat it almost like any other key. > Thus it can be explicitly associated with any address range, and can be > freed. This gives the application more flexibility and power. The > ability to free pkey-0 must be used responsibily, since pkey-0 is > associated with almost all address-range by default. > > Even with this change pkey-0 continues to be slightly more special > from the following point of view. > (a) it is implicitly allocated. > (b) it is the default key assigned to any address-range. > > Tested on powerpc.
This patch is not entirely correct. > > cc: Thomas Gleixner <tglx@linutronix.de> > cc: Dave Hansen <dave.hansen@intel.com> > cc: Michael Ellermen <mpe@ellerman.id.au> > cc: Ingo Molnar <mingo@kernel.org> > cc: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Ram Pai <linuxram@us.ibm.com> > --- > arch/powerpc/include/asm/pkeys.h | 24 ++++++++++++++++++++---- > 1 file changed, 20 insertions(+), 4 deletions(-) > > diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h > index 0409c80..9c7d3bd 100644 > --- a/arch/powerpc/include/asm/pkeys.h > +++ b/arch/powerpc/include/asm/pkeys.h > @@ -101,10 +101,18 @@ static inline u16 pte_to_pkey_bits(u64 pteflags) > > static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) > { > - /* A reserved key is never considered as 'explicitly allocated' */ > - return ((pkey < arch_max_pkey()) && > - !__mm_pkey_is_reserved(pkey) && > - __mm_pkey_is_allocated(mm, pkey)); > + /* pkey 0 is allocated by default. */ > + if (!pkey) > + return true;
This is wrong. pkey-0 should not be treated any special here. Will fix this and send a new patch. Sorry for the noise.
RP
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