[Crash-utility] [PATCHv8 2/4] crash-utility/arm64: store phy_offset and memstart_addr separately

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> > > > > @@ -1185,8 +1234,20 @@ arm64_VTOP(ulong addr)
> > > > >  			return addr - machdep->machspec->kimage_voffset;
> > > > >  		}
> > > > >
> > > > > -		if (addr >= machdep->machspec->page_offset)
> > > > > -			return addr + machdep->machspec->physvirt_offset;
> 
> I had thought it worked for all versions before commit 5383cc6efed1 (arm64: mm: Introduce vabits_actual).
> So !(machdep->flags & FLIPPED_VM) branch should use the formula.
> 
> But it turns out to be wrong. PLS see the comment followed.
> 
> > > > > +		if (addr >= machdep->machspec->page_offset) {
> > > > > +			ulong paddr;
> > > > > +
> > > > > +			if (!(machdep->flags & FLIPPED_VM) || (machdep->flags & HAS_PHYSVIRT_OFFSET))
> {
> > > > > +				paddr = addr;
> > > > > +			} else {
> > > > > +				/*
> > > > > +				 * #define __lm_to_phys(addr)	(((addr) & ~PAGE_OFFSET) +
> PHYS_OFFSET)
> > > > > +				 */
> > > > > +				paddr = addr & ~
> _PAGE_OFFSET(machdep->machspec->CONFIG_ARM64_VA_BITS);
> > > > > +			}
> > > > > +			paddr += machdep->machspec->physvirt_offset;
> > > > > +			return paddr;
> > > >
> > > > Hmm, complex.  It should be symmetric to PTOV, why differences?
> > >
> [...]
> >
> > Yes, it's one of them, and this looks better, but...
> >
> > Hmm ok, I summarized these and my question why they're asymmetric emerged:
> >
> Thank you for the patient.
> 
> > if physvirt_offset exists // HAS_PHYSVIRT_OFFSET
> >   ms->physvirt_offset = read physvirt_offset;
> > else if (machdep->flags & FLIPPED_VM)
> >   ms->physvirt_offset = ms->phys_offset_nominal;
> > else                      // !FLIPPED_VM
> >   ms->physvirt_offset = ms->phys_offset - ms->page_offset;
> >
> > PTOV:
> > if (machdep->flags & HAS_PHYSVIRT_OFFSET)
> >   v = paddr - ms->physvirt_offset;  // looks ok
> > else
> >   v = (paddr - ms->physvirt_offset) | PAGE_OFFSET;  // Is this ok when !FLIPPED_VM ?
> >
> It works for !FLIPPED_VM. But I did make a mistake on VTOP()
> 
> Flipped mm is introduced by 14c127c957c1 ("arm64: mm: Flip kernel VA space")
> 
> $ git show 14c127c957c1c6070647c171e72f06e0db275ebf:arch/arm64/include/asm/memory.h | grep "#define
> __phys_to_virt"
> #define __phys_to_virt(x)	((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
> $ git show 14c127c957c1c6070647c171e72f06e0db275ebf~1:arch/arm64/include/asm/memory.h | grep "#define
> __phys_to_virt"
> #define __phys_to_virt(x)	((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
> 
> So the formula keeps unchange across filpped-mm. The same case for VTOP.
> And what matters is physvirt_offset introduced by 5383cc6efed1 ("arm64: mm: Introduce vabits_actual")
> 
> > VTOP:
> > if (machdep->flags & HAS_PHYSVIRT_OFFSET || !(machdep->flags & FLIPPED_VM))
> >   p = vaddr + ms->physvirt_offset;  // looks ok
> > else
> >   p = (vaddr & ~PAGE_OFFSET) + ms->physvirt_offset; // looks ok
> >
> 
> Similar,
> $git show 14c127c957c1c6070647c171e72f06e0db275ebf:arch/arm64/include/asm/memory.h | grep __lm_to_phys
> #define __lm_to_phys(addr)	(((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
> 	__is_lm_address(__x) ? __lm_to_phys(__x) :			\
> $ git show 14c127c957c1c6070647c171e72f06e0db275ebf~1:arch/arm64/include/asm/memory.h | grep __lm_to_phys
> #define __lm_to_phys(addr)	(((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
> 	__is_lm_address(__x) ? __lm_to_phys(__x) :			\
> 
> >
> > When !FLIPPED_VM, PTOV calculates:
> >   v = (paddr - ms->physvirt_offset) | PAGE_OFFSET
> >     = (paddr - ms->physoffset + ms->page_offset) | PAGE_OFFSET
> >
> > This might be not wrong in the result value because of the or operation,
> > but looks wrong formula.  So PTOV also needs the !(machdep->flags & FLIPPED_VM)
> > condition?  or I'm missing something?
> >
> 
> So I need to drop the !(machdep->flags & FLIPPED_VM) in VTOP(), instead of adding in PTOV().
> Sorry for the confusion and hope I make it clear.

If you do so, you mean that you will change
  ms->physvirt_offset = ms->phys_offset - ms->page_offset
to
  ms->physvirt_offset = ms->phys_offset
if !FLIPPED_VM ?

For me, it's readable and understandable to match the formulas with kernel's
one.  In this case, use the physvirt_offset only if physvirt_offset exists.
We can do it now because we are introducing a switchable PTOV/VTOP.
For example:

ms->phys_offset_nominal = read phys_offset;
if (ms->phys_offset_nominal < 0)
  ms->phys_offset = ms->phys_offset_nominal + MEMSTART_ADDR_OFFSET;
else
  ms->phys_offset = ms->phys_offset_nominal

PTOV:
if (machdep->flags & HAS_PHYSVIRT_OFFSET)
  v = paddr - ms->physvirt_offset;
else
  v = (paddr - ms->phys_offset_nominal) | PAGE_OFFSET

VTOP:
if (machdep->flags & HAS_PHYSVIRT_OFFSET)
  p = vaddr + ms->physvirt_offset;
else
  p = (vaddr & ~PAGE_OFFSET) + ms->phys_offset_nominal;


btw, just to clarify, where is the phys_offset used except for
PTOV and VTOP?  I cannot find it..

> while getting PFN offset in a dumpfile, phys_offset is
> required.

Thanks,
Kazu