linux-kernel - Re: [PATCHv2 1/3] x86/mm: Provide pmdp

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Date:   Mon, 19 Jun 2017 15:04:22 +0200
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper

On Mon, 19 Jun 2017 15:48:19 +0300
"Kirill A. Shutemov" <kirill@...temov.name> wrote:

> On Mon, Jun 19, 2017 at 07:48:01AM +0200, Martin Schwidefsky wrote:
> > On Thu, 15 Jun 2017 17:52:22 +0300
> > "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:
> >   
> > > We need an atomic way to setup pmd page table entry, avoiding races with
> > > CPU setting dirty/accessed bits. This is required to implement
> > > pmdp_invalidate() that doesn't loose these bits.
> > > 
> > > On PAE we have to use cmpxchg8b as we cannot assume what is value of new pmd and
> > > setting it up half-by-half can expose broken corrupted entry to CPU.
> > > 
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > > Cc: Ingo Molnar <mingo@...nel.org>
> > > Cc: H. Peter Anvin <hpa@...or.com>
> > > Cc: Thomas Gleixner <tglx@...utronix.de>
> > > ---
> > >  arch/x86/include/asm/pgtable-3level.h | 18 ++++++++++++++++++
> > >  arch/x86/include/asm/pgtable.h        | 14 ++++++++++++++
> > >  2 files changed, 32 insertions(+)
> > > 
> > > diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> > > index f5af95a0c6b8..a924fc6a96b9 100644
> > > --- a/arch/x86/include/asm/pgtable.h
> > > +++ b/arch/x86/include/asm/pgtable.h
> > > @@ -1092,6 +1092,20 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
> > >  	clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp);
> > >  }
> > > 
> > > +#ifndef pmdp_establish
> > > +#define pmdp_establish pmdp_establish
> > > +static inline pmd_t pmdp_establish(pmd_t *pmdp, pmd_t pmd)
> > > +{
> > > +	if (IS_ENABLED(CONFIG_SMP)) {
> > > +		return xchg(pmdp, pmd);
> > > +	} else {
> > > +		pmd_t old = *pmdp;
> > > +		*pmdp = pmd;
> > > +		return old;
> > > +	}
> > > +}
> > > +#endif
> > > +
> > >  /*
> > >   * clone_pgd_range(pgd_t *dst, pgd_t *src, int count);
> > >   *  
> > 
> > For the s390 version of the pmdp_establish function we need the mm to be able
> > to do the TLB flush correctly. Can we please add a "struct vm_area_struct *vma"
> > argument to pmdp_establish analog to pmdp_invalidate?
> > 
> > The s390 patch would then look like this:
> > --
> > From 4d4641249d5e826c21c522d149553e89d73fcd4f Mon Sep 17 00:00:00 2001
> > From: Martin Schwidefsky <schwidefsky@...ibm.com>
> > Date: Mon, 19 Jun 2017 07:40:11 +0200
> > Subject: [PATCH] s390/mm: add pmdp_establish
> > 
> > Define the pmdp_establish function to replace a pmd entry with a new
> > one and return the old value.
> > 
> > Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> > ---
> >  arch/s390/include/asm/pgtable.h | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> > index bb59a0aa3249..dedeecd5455c 100644
> > --- a/arch/s390/include/asm/pgtable.h
> > +++ b/arch/s390/include/asm/pgtable.h
> > @@ -1511,6 +1511,13 @@ static inline void pmdp_invalidate(struct vm_area_struct *vma,
> >  	pmdp_xchg_direct(vma->vm_mm, addr, pmdp, __pmd(_SEGMENT_ENTRY_EMPTY));
> >  }
> >  
> > +static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
> > +				   pmd_t *pmdp, pmd_t pmd)
> > +{
> > +	return pmdp_xchg_direct(vma->vm_mm, addr, pmdp, pmd);  
> 
> I guess, you need address too :-P.
> 
> I'll change prototype of pmdp_establish() and apply your patch.
 
Ahh, yes. vma + addr please ;-)

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.