linux-kernel - Re: [PATCH v2 3/4] arm64: decouple check whether pfn is in linear map from pfn

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Message-ID: <YIAYYcWtuwszHMux@kernel.org>
Date:   Wed, 21 Apr 2021 15:19:45 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        David Hildenbrand <david@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 3/4] arm64: decouple check whether pfn is in linear
 map from pfn_valid()

On Wed, Apr 21, 2021 at 04:29:48PM +0530, Anshuman Khandual wrote:
> 
> On 4/21/21 12:21 PM, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@...ux.ibm.com>
> > 
> > The intended semantics of pfn_valid() is to verify whether there is a
> > struct page for the pfn in question and nothing else.
> > 
> > Yet, on arm64 it is used to distinguish memory areas that are mapped in the
> > linear map vs those that require ioremap() to access them.
> > 
> > Introduce a dedicated pfn_is_map_memory() wrapper for
> > memblock_is_map_memory() to perform such check and use it where
> > appropriate.
> > 
> > Using a wrapper allows to avoid cyclic include dependencies.
> > 
> > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> > ---
> >  arch/arm64/include/asm/memory.h |  2 +-
> >  arch/arm64/include/asm/page.h   |  1 +
> >  arch/arm64/kvm/mmu.c            |  2 +-
> >  arch/arm64/mm/init.c            | 11 +++++++++++
> >  arch/arm64/mm/ioremap.c         |  4 ++--
> >  arch/arm64/mm/mmu.c             |  2 +-
> >  6 files changed, 17 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > index 0aabc3be9a75..194f9f993d30 100644
> > --- a/arch/arm64/include/asm/memory.h
> > +++ b/arch/arm64/include/asm/memory.h
> > @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x)
> >  
> >  #define virt_addr_valid(addr)	({					\
> >  	__typeof__(addr) __addr = __tag_reset(addr);			\
> > -	__is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr));	\
> > +	__is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr));	\
> >  })
> >  
> >  void dump_mem_limit(void);
> > diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
> > index 012cffc574e8..99a6da91f870 100644
> > --- a/arch/arm64/include/asm/page.h
> > +++ b/arch/arm64/include/asm/page.h
> > @@ -38,6 +38,7 @@ void copy_highpage(struct page *to, struct page *from);
> >  typedef struct page *pgtable_t;
> >  
> >  extern int pfn_valid(unsigned long);
> > +extern int pfn_is_map_memory(unsigned long);
> 
> Check patch is complaining about this.
> 
> WARNING: function definition argument 'unsigned long' should also have an identifier name
> #50: FILE: arch/arm64/include/asm/page.h:41:
> +extern int pfn_is_map_memory(unsigned long);
> 
> 
> >  
> >  #include <asm/memory.h>
> >  
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 8711894db8c2..23dd99e29b23 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -85,7 +85,7 @@ void kvm_flush_remote_tlbs(struct kvm *kvm)
> >  
> >  static bool kvm_is_device_pfn(unsigned long pfn)
> >  {
> > -	return !pfn_valid(pfn);
> > +	return !pfn_is_map_memory(pfn);
> >  }
> >  
> >  /*
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 3685e12aba9b..dc03bdc12c0f 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -258,6 +258,17 @@ int pfn_valid(unsigned long pfn)
> >  }
> >  EXPORT_SYMBOL(pfn_valid);
> >  
> > +int pfn_is_map_memory(unsigned long pfn)
> > +{
> > +	phys_addr_t addr = PFN_PHYS(pfn);
> > +
> 
> Should also bring with it, the comment regarding upper bits in
> the pfn from arm64 pfn_valid().

I think a reference to the comment in pfn_valid() will suffice.

BTW, I wonder how is that other architectures do not need this check?
 
> > +	if (PHYS_PFN(addr) != pfn)
> > +		return 0;
> > +	
> 
>  ^^^^^ trailing spaces here.
> 
> ERROR: trailing whitespace
> #81: FILE: arch/arm64/mm/init.c:263:
> +^I$

Oops :)
 
> > +	return memblock_is_map_memory(addr);
> > +}
> > +EXPORT_SYMBOL(pfn_is_map_memory);
> > +
> 
> Is the EXPORT_SYMBOL() required to build drivers which will use
> pfn_is_map_memory() but currently use pfn_valid() ?

Yes, this is required for virt_addr_valid() that is used by modules.

-- 
Sincerely yours,
Mike.