Re: [PATCH v3] x86: treat pkey-0 special
From: Thomas Gleixner <hidden>
Date: 2018-03-15 09:46:36
Also in:
linux-arch, linux-mm, lkml
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 EllermenPlease 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.
quoted hunk ↗ jump to hunk
cc: Dave Hansen <redacted> cc: Michael Ellermen <mpe@ellerman.id.au> cc: Ingo Molnar <mingo@kernel.org> Signed-off-by: Ram Pai <redacted> --- 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