Re: [PATCHv2 6/6] arm64: Add support for CONFIG_DEBUG_VIRTUAL

[Laura Abbott]

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