Re: [PATCH v2 3/4] arm64: decouple check whether pfn is in linear map from pfn_valid()

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 4/21/21 5:49 PM, Mike Rapoport wrote:
> 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@linux.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@linux.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.

Okay.

> 
> BTW, I wonder how is that other architectures do not need this check?

Trying to move that into generic pfn_valid() in mmzone.h, will resend
the RFC patch after this series.

https://patchwork.kernel.org/project/linux-mm/patch/1615174073-10520-1-git-send-email-anshuman.khandual@arm.com/

>  
>>> +	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.
> 

There will be two adjacent EXPORT_SYMBOLS(), one for pfn_valid() and
one for pfn_is_map_memory(). But its okay I guess, cant help it.

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