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SubjectRe: [RFC/RFT PATCH 2/3] arm64: decouple check whether pfn is normal memory from pfn_valid()
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On 14.04.21 22:29, Mike Rapoport wrote:
> On Wed, Apr 14, 2021 at 05:58:26PM +0200, David Hildenbrand wrote:
>> On 08.04.21 07:14, Anshuman Khandual wrote:
>>>
>>> On 4/7/21 10:56 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.
>>>
>>> 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@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 | 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.
>
> Yeah, at the moment NOMAP is very much arm specific so I'd keep it this way
> for now.
>
>> 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.
>
> In my current version (to be posted soon) I've started with
> pfn_lineary_mapped() but then ended up with pfn_mapped() to make it
> "upward" compatible with architectures that use direct rather than linear
> map :)

And even that is moot. It doesn't tell you if a PFN is *actually* mapped
(hello secretmem).

I'd suggest to just use memblock_is_map_memory() in arch specific code.
Then it's clear what we are querying exactly and what the semantics
might be.

--
Thanks,

David / dhildenb

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