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Date:   Wed, 13 Jun 2018 23:13:56 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Kai Huang <kai.huang@linux.intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv3 01/17] mm: Do no merge VMAs with different encryption
 KeyIDs
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On Wed, Jun 13, 2018 at 05:45:24PM +0000, Dave Hansen wrote:
> On 06/12/2018 07:38 AM, Kirill A. Shutemov wrote:
> > VMAs with different KeyID do not mix together. Only VMAs with the same
> > KeyID are compatible.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> >  include/linux/mm.h | 7 +++++++
> >  mm/mmap.c          | 3 ++-
> >  2 files changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 02a616e2f17d..1c3c15f37ed6 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1492,6 +1492,13 @@ static inline bool vma_is_anonymous(struct vm_area_struct *vma)
> >  	return !vma->vm_ops;
> >  }
> >  
> > +#ifndef vma_keyid
> > +static inline int vma_keyid(struct vm_area_struct *vma)
> > +{
> > +	return 0;
> > +}
> > +#endif
> 
> I'm generally not a fan of this #ifdef'ing method.  It makes it hard to
> figure out who is supposed to define it, and it's also substantially
> more fragile in the face of #include ordering.
> 
> I'd much rather see some Kconfig involvement, like
> CONFIG_ARCH_HAS_MEM_ENCRYPTION or something.

Well, it's matter of taste, I guess. I do prefer per-function #ifdef'ing.
It seems more flexible to me.

I can rework it if maintainers prefer to see config option instead.

-- 
 Kirill A. Shutemov