linux-kernel - Re: [PATCH v13 3/3] arm64: Implement page table free interfaces

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Message-ID: <20180921095607.GA166997@arrakis.emea.arm.com>
Date:   Fri, 21 Sep 2018 10:56:07 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Chintan Pandya <cpandya@...eaurora.org>
Cc:     mark.rutland@....com, toshi.kani@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v13 3/3] arm64: Implement page table free interfaces

On Thu, Sep 20, 2018 at 06:25:29PM +0100, Catalin Marinas wrote:
> On Wed, Jun 06, 2018 at 12:31:21PM +0530, Chintan Pandya wrote:
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 8ae5d7a..65f8627 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -45,6 +45,7 @@
> >  #include <asm/memblock.h>
> >  #include <asm/mmu_context.h>
> >  #include <asm/ptdump.h>
> > +#include <asm/tlbflush.h>
> >  
> >  #define NO_BLOCK_MAPPINGS	BIT(0)
> >  #define NO_CONT_MAPPINGS	BIT(1)
> > @@ -977,12 +978,51 @@ int pmd_clear_huge(pmd_t *pmdp)
> >  	return 1;
> >  }
> >  
> > -int pud_free_pmd_page(pud_t *pud, unsigned long addr)
> > +int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
> >  {
> > -	return pud_none(*pud);
> > +	pte_t *table;
> > +	pmd_t pmd;
> > +
> > +	pmd = READ_ONCE(*pmdp);
> > +
> > +	/* No-op for empty entry and WARN_ON for valid entry */
> > +	if (!pmd_present(pmd) || !pmd_table(pmd)) {
> > +		VM_WARN_ON(!pmd_table(pmd));
> > +		return 1;
> > +	}
> 
> What's this VM_WARN_ON supposed to do here? If the pmd is 0, we trigger
> it all the time. Did you actually mean something like:
> 
> 		VM_WARN_ON(!pmd_none(pmd));
> 
> or pmd_present(pmd)?
> 
> Since the comment mentions empty entry, I'd rather make it explicit:
> 
> 	if (pmd_none(pmd) || !pmd_table(pmd))
> 		VM_WARN_ON(!pmd_none(pmd));
> 		return 1;
> 	}

Ignore this, fixed in -rc4 (fac880c7d074 "arm64: fix erroneous warnings
in page freeing functions").

-- 
Catalin