linux-kernel - Re: [RFC v5 11/38] mm: introduce an additional vma bit for powerpc pkey

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Date:   Wed, 12 Jul 2017 15:23:31 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, arnd@...db.de,
        akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v5 11/38] mm: introduce an additional vma bit for powerpc
 pkey

On Tue, Jul 11, 2017 at 11:10:46AM -0700, Dave Hansen wrote:
> On 07/05/2017 02:21 PM, Ram Pai wrote:
> > Currently there are only 4bits in the vma flags to support 16 keys
> > on x86.  powerpc supports 32 keys, which needs 5bits. This patch
> > introduces an addition bit in the vma flags.
> > 
> > Signed-off-by: Ram Pai <linuxram@...ibm.com>
> > ---
> >  fs/proc/task_mmu.c |    6 +++++-
> >  include/linux/mm.h |   18 +++++++++++++-----
> >  2 files changed, 18 insertions(+), 6 deletions(-)
> > 
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index f0c8b33..2ddc298 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -666,12 +666,16 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> >  		[ilog2(VM_MERGEABLE)]	= "mg",
> >  		[ilog2(VM_UFFD_MISSING)]= "um",
> >  		[ilog2(VM_UFFD_WP)]	= "uw",
> > -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> > +#ifdef CONFIG_ARCH_HAS_PKEYS
> >  		/* These come out via ProtectionKey: */
> >  		[ilog2(VM_PKEY_BIT0)]	= "",
> >  		[ilog2(VM_PKEY_BIT1)]	= "",
> >  		[ilog2(VM_PKEY_BIT2)]	= "",
> >  		[ilog2(VM_PKEY_BIT3)]	= "",
> > +#endif /* CONFIG_ARCH_HAS_PKEYS */
> > +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> > +		/* Additional bit in ProtectionKey: */
> > +		[ilog2(VM_PKEY_BIT4)]	= "",
> >  #endif
> 
> I'd probably just leave the #ifdef out and eat the byte or whatever of
> storage that this costs us on x86.

fine with me.

> 
> >  	};
> >  	size_t i;
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 7cb17c6..3d35bcc 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -208,21 +208,29 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
> >  #define VM_HIGH_ARCH_BIT_1	33	/* bit only usable on 64-bit architectures */
> >  #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
> >  #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
> > +#define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit arch */
> 
> Please just copy the above lines.

Just copying over makes checkpatch.pl unhappy. It exceeds 80 columns.

> 
> >  #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
> >  #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
> >  #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
> >  #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
> > +#define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
> >  #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
> >  
> > -#if defined(CONFIG_X86)
> > -# define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
> > -#if defined (CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS)
> > +#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 */
> > +# 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
> > -#endif
> > +#endif /* CONFIG_ARCH_HAS_PKEYS */
> 
> We have the space here, so can we just say that it's 4-bits on x86 and 5
> on ppc?

sure.

> 
> > +#if defined(CONFIG_PPC64_MEMORY_PROTECTION_KEYS)
> > +# define VM_PKEY_BIT4	VM_HIGH_ARCH_4 /* additional key bit used on ppc64 */
> > +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> 
> Why bother #ifdef'ing a #define?

ok. 

RP