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

[Mike Rapoport]

On Thu, Apr 08, 2021 at 10:44:58AM +0530, 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 ?

Yeah, that would have been helpful :)
 
> > 
> > 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.

As NOMAP itself is quite ARM specific, this check is currently only
relevant for arm64 and maybe arm32.
But probably having an EXPORT_SYMBOL wrapper for memblock_is_map_memory(),
say in memblock does make sense for all architectures that have
KEEP_MEMBLOCK.

> 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.

Yeah, I agree that naming could be better here. I think that for a generic name
we'd need pfn_is_directly_mapped() so that it can be used on x86 ;-)
 
> >  static phys_addr_t memory_limit = PHYS_ADDR_MAX;
> >  
> >  /*
> > diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
> > index b5e83c46b23e..82a369b22ef5 100644
> > --- a/arch/arm64/mm/ioremap.c
> > +++ b/arch/arm64/mm/ioremap.c
> > @@ -43,7 +43,7 @@ static void __iomem *__ioremap_caller(phys_addr_t phys_addr, size_t size,
> >  	/*
> >  	 * Don't allow RAM to be mapped.
> >  	 */
> > -	if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
> > +	if (WARN_ON(pfn_is_memory(__phys_to_pfn(phys_addr))))
> >  		return NULL;
> >  
> >  	area = get_vm_area_caller(size, VM_IOREMAP, caller);
> > @@ -84,7 +84,7 @@ EXPORT_SYMBOL(iounmap);
> >  void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size)
> >  {
> >  	/* For normal memory we already have a cacheable mapping. */
> > -	if (pfn_valid(__phys_to_pfn(phys_addr)))
> > +	if (pfn_is_memory(__phys_to_pfn(phys_addr)))
> >  		return (void __iomem *)__phys_to_virt(phys_addr);
> >  
> >  	return __ioremap_caller(phys_addr, size, __pgprot(PROT_NORMAL),
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 5d9550fdb9cf..038d20fe163f 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -81,7 +81,7 @@ void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
> >  pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
> >  			      unsigned long size, pgprot_t vma_prot)
> >  {
> > -	if (!pfn_valid(pfn))
> > +	if (!pfn_is_memory(pfn))
> >  		return pgprot_noncached(vma_prot);
> >  	else if (file->f_flags & O_SYNC)
> >  		return pgprot_writecombine(vma_prot);
> > 

-- 
Sincerely yours,
Mike.