Re: [RFC][PATCH] arm64: Add support for CONFIG_DEBUG_VIRTUAL

[Laura Abbott]

> > > diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
> > > new file mode 100644
> > > index 0000000..6c271e2
> > > --- /dev/null
> > > +++ b/arch/arm64/mm/physaddr.c
> > > @@ -0,0 +1,17 @@
> > > +#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 bit check ensures this is the right range */
> > > +        return (__x & ~PAGE_OFFSET) + PHYS_OFFSET;
> > > +    } else {
> > > +        VIRTUAL_BUG_ON(x < kimage_vaddr || x > (unsigned long)_end);
> >
> > IIUC, in (3) you were asking if the last check should be '>' or '>='?
> >
> > To match high_memory, I suspect the latter, as _end doesn't fall within
> > the mapped virtual address space.
>
> I was actually concerned about if _end would be correct with KASLR.
> Ard confirmed that it gets fixed up to be correct. I'll change the
> check to check for >=.

While testing this, I found two places with __pa(_end) to get bounds,
one in arm64 code and one in memblock code. x86 gets away with this
because memblock is actually __pa_symbol and x86 does image placement
different and can check against the maximum image size. I think
including _end in __pa_symbol but excluding it from the generic
__virt_to_phys makes sense. It's a bit nicer than doing _end - 1 +
1 everywhere.

Thanks,
Laura