linux-kernel - Re: [PATCHv3 1/3] x86/mm/encrypt: Move page table helpers into separate translation unit

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Date:   Wed, 31 Jan 2018 01:28:00 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/3] x86/mm/encrypt: Move page table helpers into
 separate translation unit

On Tue, Jan 30, 2018 at 04:26:03PM -0600, Tom Lendacky wrote:
> On 1/24/2018 10:36 AM, Kirill A. Shutemov wrote:
> > There are bunch of functions in mem_encrypt.c that operate on the
> > identity mapping, which means they want virtual addresses to be equal to
> > physical one, without PAGE_OFFSET shift.
> > 
> > We also need to avoid paravirtualizaion call there.
> > 
> > Getting this done is tricky. We cannot use usual page table helpers.
> > It forces us to open-code a lot of things. It makes code ugly and hard
> > to modify.
> > 
> > We can get it work with the page table helpers, but it requires few
> > preprocessor tricks. These tricks may have side effects for the rest of
> > the file.
> > 
> > Let's isolate such functions into own translation unit.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> Just one minor comment at the end.  With that change:
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> 
> > ---
> >  arch/x86/mm/Makefile               |  14 +-
> >  arch/x86/mm/mem_encrypt.c          | 578 +----------------------------------
> >  arch/x86/mm/mem_encrypt_identity.c | 596 +++++++++++++++++++++++++++++++++++++
> >  arch/x86/mm/mm_internal.h          |   1 +
> >  4 files changed, 607 insertions(+), 582 deletions(-)
> >  create mode 100644 arch/x86/mm/mem_encrypt_identity.c
> > 
> 
> ...
> 
> > diff --git a/arch/x86/mm/mm_internal.h b/arch/x86/mm/mm_internal.h
> > index 4e1f6e1b8159..7b4fc4386d90 100644
> > --- a/arch/x86/mm/mm_internal.h
> > +++ b/arch/x86/mm/mm_internal.h
> > @@ -19,4 +19,5 @@ extern int after_bootmem;
> >  
> >  void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
> >  
> > +extern bool sev_enabled __section(.data);
> 
> Lets move this into arch/x86/include/asm/mem_encrypt.h and then add
> #include <linux/mem_encrypt.h> to mem_encrypt_identity.c.

Why? Will we need it beyond arch/x86/mm/ in the future?

-- 
 Kirill A. Shutemov