Re: [PATCHv4 07/10] kexec: Switch to __pa_symbol

[Eric W. Biederman]

Dave Young <dyoung@xxxxxxxxxx> writes:

> Hi, Laura
> On 11/29/16 at 10:55am, Laura Abbott wrote:
>> 
>> __pa_symbol is the correct api to get the physical address of kernel
>> symbols. Switch to it to allow for better debug checking.
>> 
>
> I assume __pa_symbol is faster than __pa, but it still need some testing
> on all arches which support kexec.
>
> But seems long long ago there is a commit e3ebadd95cb in the commit log
> I see below from:
> "we should deprecate __pa_symbol(), and preferably __pa() too - and
>  just use "virt_to_phys()" instead, which is is more readable and has
>  nicer semantics."
>
> But maybe in modern code __pa_symbol is prefered I may miss background.
> virt_to_phys still sounds more readable now for me though.

There has been a lot of history with the various definitions.
__pa_symbol used to be x86 specific.

Now what we have is that __pa_symbol is just __pa(RELOC_HIDE(x));

Now arguably that whole reloc hide thing should happen by architectures
having a non-inline version of __pa as was done in the commit you
mention.  But at this point there appears to be nothing wrong with
changing a __pa to a __pa_symbol it might make things a tad more
reliable depending on the implementation of __pa.

Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>


Eric

>> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
>> ---
>> Found during review of the kernel. Untested.
>> ---
>>  kernel/kexec_core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index 5616755..e1b625e 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -1397,7 +1397,7 @@ void __weak arch_crash_save_vmcoreinfo(void)
>>  
>>  phys_addr_t __weak paddr_vmcoreinfo_note(void)
>>  {
>> -	return __pa((unsigned long)(char *)&vmcoreinfo_note);
>> +	return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
>>  }
>>  
>>  static int __init crash_save_vmcoreinfo_init(void)
>> -- 
>> 2.7.4
>> 
>> 
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>
> Thanks
> Dave