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

From: ebiederm@xmission.com (Eric W. Biederman)
To: Dave Young <dyoung@redhat.com>
Cc: Laura Abbott <labbott@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Will Deacon <will.deacon@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	x86@kernel.org, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [PATCHv4 07/10] kexec: Switch to __pa_symbol
Date: Wed, 30 Nov 2016 21:13:24 -0600	[thread overview]
Message-ID: <87polc7357.fsf@xmission.com> (raw)
In-Reply-To: <20161201024103.GA32438@dhcp-128-65.nay.redhat.com> (Dave Young's message of "Thu, 1 Dec 2016 10:41:03 +0800")

Dave Young <dyoung@redhat.com> 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@xmission.com>

Eric

>> Signed-off-by: Laura Abbott <labbott@redhat.com>
>> ---
>> 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
>> 
>> 
>> _______________________________________________
>> kexec mailing list
>> kexec@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec
>
> Thanks
> Dave