On Wed, 14 Mar 2018, 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. > > This patch clarifies the semantics of pkey-0 and provides the
grep 'This patch' Documentation/process > corresponding implementation on powerpc. > > Pkey-0 is special with the following semantics. > (a) it is implicitly allocated and can never be freed. It always exists. > (b) it is the default key assigned to any address-range. > (c) it can be explicitly associated with any address-range. > > Tested on x86_64. I'm curious how the corresponding implementation on powerpc can be tested on x86_64. Copy and paste is not enough ... > > History: > v3 : added clarification of the semantics of pkey0. > -- suggested by Dave Hansen > v2 : split the patch into two, one for x86 and one for powerpc > -- suggested by Michael Ellermen Please put the history below the --- seperator. It's not part of the changelog. That way the tools can discard it when picking up the patch. > > cc: Dave Hansen <[email protected]> > cc: Michael Ellermen <[email protected]> > cc: Ingo Molnar <[email protected]> > Signed-off-by: Ram Pai <[email protected]> > --- > arch/x86/include/asm/pkeys.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h > index a0ba1ff..6ea7486 100644 > --- a/arch/x86/include/asm/pkeys.h > +++ b/arch/x86/include/asm/pkeys.h > @@ -52,7 +52,7 @@ bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) > * from pkey_alloc(). pkey 0 is special, and never > * returned from pkey_alloc(). > */ > - if (pkey <= 0) > + if (pkey < 0) > return false; > if (pkey >= arch_max_pkey()) > return false; > @@ -92,7 +92,8 @@ int mm_pkey_alloc(struct mm_struct *mm) > static inline > int mm_pkey_free(struct mm_struct *mm, int pkey) > { > - if (!mm_pkey_is_allocated(mm, pkey)) > + /* pkey 0 is special and can never be freed */ This comment is pretty useless. How should anyone figure out whats special about pkey 0? > + if (!pkey || !mm_pkey_is_allocated(mm, pkey)) Why this extra check? mm_pkey_is_allocated(mm, 0) should not return true ever. If it does, then this wants to be fixed. Thanks, tglx
