diff mbox

[v13,3/3] mm, powerpc, x86: introduce an additional vma bit for powerpc pkey

Message ID 1525471183-21277-3-git-send-email-linuxram@us.ibm.com (mailing list archive)
State New, archived
Headers show

Commit Message

Ram Pai May 4, 2018, 9:59 p.m. UTC 
Only 4bits are allocated in the vma flags to hold 16 keys. This is
sufficient on x86. PowerPC supports 32 keys, which needs 5bits.
Allocate an  additional bit.

cc: Dave Hansen <dave.hansen@intel.com>
cc: Michael Ellermen <mpe@ellerman.id.au>
cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
cc: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
 fs/proc/task_mmu.c |    1 +
 include/linux/mm.h |    8 +++++++-
 2 files changed, 8 insertions(+), 1 deletions(-)

Comments

Dave Hansen May 4, 2018, 10:57 p.m. UTC | #1 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 0c9e392..3ddddc7 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -679,6 +679,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>  		[ilog2(VM_PKEY_BIT1)]	= "",
>  		[ilog2(VM_PKEY_BIT2)]	= "",
>  		[ilog2(VM_PKEY_BIT3)]	= "",
> +		[ilog2(VM_PKEY_BIT4)]	= "",
>  #endif /* CONFIG_ARCH_HAS_PKEYS */
...
> +#if defined(CONFIG_PPC)
> +# define VM_PKEY_BIT4	VM_HIGH_ARCH_4
> +#else 
> +# define VM_PKEY_BIT4	0
> +#endif
>  #endif /* CONFIG_ARCH_HAS_PKEYS */

That new line boils down to:

		[ilog2(0)]	= "",

on x86.  It wasn't *obvious* to me that it is OK to do that.  The other
possibly undefined bits (VM_SOFTDIRTY for instance) #ifdef themselves
out of this array.

I would just be a wee bit worried that this would overwrite the 0 entry
("??") with "".
Ram Pai May 5, 2018, 1:12 a.m. UTC | #2 
On Fri, May 04, 2018 at 03:57:33PM -0700, Dave Hansen wrote:
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 0c9e392..3ddddc7 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -679,6 +679,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> >  		[ilog2(VM_PKEY_BIT1)]	= "",
> >  		[ilog2(VM_PKEY_BIT2)]	= "",
> >  		[ilog2(VM_PKEY_BIT3)]	= "",
> > +		[ilog2(VM_PKEY_BIT4)]	= "",
> >  #endif /* CONFIG_ARCH_HAS_PKEYS */
> ...
> > +#if defined(CONFIG_PPC)
> > +# define VM_PKEY_BIT4	VM_HIGH_ARCH_4
> > +#else 
> > +# define VM_PKEY_BIT4	0
> > +#endif
> >  #endif /* CONFIG_ARCH_HAS_PKEYS */
> 
> That new line boils down to:
> 
> 		[ilog2(0)]	= "",
> 
> on x86.  It wasn't *obvious* to me that it is OK to do that.  The other
> possibly undefined bits (VM_SOFTDIRTY for instance) #ifdef themselves
> out of this array.
> 
> I would just be a wee bit worried that this would overwrite the 0 entry
> ("??") with "".

Yes it would :-( and could potentially break anything that depends on
0th entry being "??"

Is the following fix acceptable?

#if VM_PKEY_BIT4
                [ilog2(VM_PKEY_BIT4)]   = "",
#endif
Dave Hansen May 5, 2018, 4:42 a.m. UTC | #3 
On 05/04/2018 06:12 PM, Ram Pai wrote:
>> That new line boils down to:
>>
>> 		[ilog2(0)]	= "",
>>
>> on x86.  It wasn't *obvious* to me that it is OK to do that.  The other
>> possibly undefined bits (VM_SOFTDIRTY for instance) #ifdef themselves
>> out of this array.
>>
>> I would just be a wee bit worried that this would overwrite the 0 entry
>> ("??") with "".
> Yes it would :-( and could potentially break anything that depends on
> 0th entry being "??"
> 
> Is the following fix acceptable?
> 
> #if VM_PKEY_BIT4
>                 [ilog2(VM_PKEY_BIT4)]   = "",
> #endif

Yep, I think that works for me.
diff mbox

Patch

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 0c9e392..3ddddc7 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -679,6 +679,7 @@  static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_PKEY_BIT1)]	= "",
 		[ilog2(VM_PKEY_BIT2)]	= "",
 		[ilog2(VM_PKEY_BIT3)]	= "",
+		[ilog2(VM_PKEY_BIT4)]	= "",
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 	};
 	size_t i;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c6a6f24..cca67d1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -230,10 +230,16 @@  extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
 # define VM_PKEY_SHIFT	VM_HIGH_ARCH_BIT_0
-# define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 4-bit value */
+/* Protection key is a 4-bit value on x86 and 5-bit value on ppc64   */
+# define VM_PKEY_BIT0	VM_HIGH_ARCH_0
 # define VM_PKEY_BIT1	VM_HIGH_ARCH_1
 # define VM_PKEY_BIT2	VM_HIGH_ARCH_2
 # define VM_PKEY_BIT3	VM_HIGH_ARCH_3
+#if defined(CONFIG_PPC)
+# define VM_PKEY_BIT4	VM_HIGH_ARCH_4
+#else 
+# define VM_PKEY_BIT4	0
+#endif
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 
 #if defined(CONFIG_X86)