linux-kernel - Re: [PATCHv2 6/6] arm64: Add support for CONFIG_DEBUG

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Date:   Wed, 2 Nov 2016 18:05:38 -0600
From:   Laura Abbott <labbott@...hat.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv2 6/6] arm64: Add support for CONFIG_DEBUG_VIRTUAL

On 11/02/2016 05:06 PM, Mark Rutland wrote:
> On Wed, Nov 02, 2016 at 03:00:54PM -0600, Laura Abbott wrote:
>> +CFLAGS_physaddr.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
>> +obj-$(CONFIG_DEBUG_VIRTUAL)	+= physaddr.o
>
>> diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
>> new file mode 100644
>> index 0000000..874c782
>> --- /dev/null
>> +++ b/arch/arm64/mm/physaddr.c
>> @@ -0,0 +1,34 @@
>> +#include <linux/mm.h>
>> +
>> +#include <asm/memory.h>
>> +
>> +unsigned long __virt_to_phys(unsigned long x)
>> +{
>> +	phys_addr_t __x = (phys_addr_t)x;
>> +
>> +	if (__x & BIT(VA_BITS - 1)) {
>> +		/*
>> +		 * The linear kernel range starts in the middle of the virtual
>> +		 * adddress space. Testing the top bit for the start of the
>> +		 * region is a sufficient check.
>> +		 */
>> +		return (__x & ~PAGE_OFFSET) + PHYS_OFFSET;
>> +	} else {
>> +		VIRTUAL_BUG_ON(x < kimage_vaddr || x >= (unsigned long)_end);
>> +		return (__x - kimage_voffset);
>> +	}
>> +}
>> +EXPORT_SYMBOL(__virt_to_phys);
>> +
>> +unsigned long __phys_addr_symbol(unsigned long x)
>> +{
>> +	phys_addr_t __x = (phys_addr_t)x;
>> +
>> +	/*
>> +	 * This is intentionally different than above to be a tighter check
>> +	 * for symbols.
>> +	 */
>> +	VIRTUAL_BUG_ON(x < kimage_vaddr + TEXT_OFFSET || x > (unsigned long) _end);
>
> Can't we use _text instead of kimage_vaddr + TEXT_OFFSET? That way we don't
> need CFLAGS_physaddr.o.
>
> Or KERNEL_START / KERNEL_END from <asm/memory.h>?
>
> Otherwise, this looks good to me (though I haven't grokked the need for
> __pa_symbol() yet).

I guess it's a question of what's clearer. I like kimage_vaddr +
TEXT_OFFSET because it clearly states we are checking from the
start of the kernel image vs. _text only shows the start of the
text region. Yes, it's technically the same but a little less
obvious. I suppose that could be solved with some more elaboration
in the comment.

Thanks,
Laura

>
> Thanks,
> Mark.
>
>> +	return (__x - kimage_voffset);
>> +}
>> +EXPORT_SYMBOL(__phys_addr_symbol);
>> --
>> 2.10.1
>>