Re: [RFC/RFT PATCH 2/3] arm64: decouple check whether pfn is normal memory from pfn_valid()

[David Hildenbrand]

On 08.04.21 07:14, Anshuman Khandual wrote:
> On 4/7/21 10:56 PM, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> >
> > The intended semantics of pfn_valid() is to verify whether there is a
> > struct page for the pfn in question and nothing else.
>
> Should there be a comment affirming this semantics interpretation, above the
> generic pfn_valid() in include/linux/mmzone.h ?
>
> > 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_memory() to perform such check and use it
> > where appropriate.
> >
> > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > ---
> >   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            | 6 ++++++
> >   arch/arm64/mm/ioremap.c         | 4 ++--
> >   arch/arm64/mm/mmu.c             | 2 +-
> >   6 files changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > index 0aabc3be9a75..7e77fdf71b9d 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_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..32b485bcc6ff 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_memory(unsigned long);
> >   
> >   #include <asm/memory.h>
> >   
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 8711894db8c2..ad2ea65a3937 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_memory(pfn);
> >   }
> >   
> >   /*
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 3685e12aba9b..258b1905ed4a 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -258,6 +258,12 @@ int pfn_valid(unsigned long pfn)
> >   }
> >   EXPORT_SYMBOL(pfn_valid);
> >   
> > +int pfn_is_memory(unsigned long pfn)
> > +{
> > +	return memblock_is_map_memory(PFN_PHYS(pfn));
> > +}
> > +EXPORT_SYMBOL(pfn_is_memory);> +
>
> Should not this be generic though ? There is nothing platform or arm64
> specific in here. Wondering as pfn_is_memory() just indicates that the
> pfn is linear mapped, should not it be renamed as pfn_is_linear_memory()
> instead ? Regardless, it's fine either way.

TBH, I dislike (generic) pfn_is_memory(). It feels like we're mixing 
concepts. NOMAP memory vs !NOMAP memory; even NOMAP is some kind of 
memory after all. pfn_is_map_memory() would be more expressive, although 
still sub-optimal.

We'd actually want some kind of arm64-specific pfn_is_system_memory() or 
the inverse pfn_is_device_memory() -- to be improved.

--
Thanks,

David / dhildenb