[Crash-utility] [PATH v4 2/2] arm64: add 4-level translation

[Dave Anderson]

----- Original Message -----
> On Wed, Jun 01, 2016 at 10:32:56AM -0400, Dave Anderson wrote:
> > 
> > ----- Original Message -----
> > > On Tue, May 31, 2016 at 03:30:44PM -0400, Dave Anderson wrote:
> > > > 
> > > > This patch looks good -- if it wasn't layered on top of the KASLR
> > > > patch,
> > > > I would check it into github.
> > > 
> > > This patch is almost independent from KASLR support, except that
> > > adding new flags, VM_L4_4K and NEW_VMEMMAP, is conflicting.
> > > 
> > > When you merge it, please make a change.
> > > 
> > > -Takahiro AKASHI
> > 
> > OK, I see that now.  But upon further inspection, I've got another question
> > about this piece:
> > 
> >  + * 4-levels / 4K pages
> >  + * 48-bit VA
> >  + */
> >  +#define PTRS_PER_PGD_L4_4K   ((1UL) << (48 - 39))
> >  +#define PTRS_PER_PUD_L4_4K   (512)
> >  +#define PTRS_PER_PMD_L4_4K   (512)
> >  +#define PTRS_PER_PTE_L4_4K   (512)
> >  +#define PGDIR_SHIFT_L4_4K    (39)
> >  +#define PGDIR_SIZE_L4_4K     ((1UL) << PGDIR_SHIFT_L4_4K)
> >  +#define PGDIR_MASK_L4_4K     (~(PGDIR_SIZE_L4_4K-1))
> >  +#define PUD_SHIFT_L4_4K      (30)
> >  +#define PUD_SIZE_L4_4K       ((1UL) << PUD_SHIFT_L4_4K)
> >  +#define PUD_MASK_L4_4K       (~(PUD_SIZE_L4_4K-1))
> >  +#define PMD_SHIFT_L4_4K      (21)
> >  +#define PMD_SIZE_L4_4K       (1UL << PMD_SHIFT_L4_4K)
> >  +#define PMD_MASK_L4_4K       (~(PMD_SIZE_L4_4K-1))
> >  +
> >  +#define PGDIR_SIZE      (1UL << ((48 - 39) + 3))
> >  +#define PGDIR_MASK      (~(PGDIR_SIZE - 1))
> >  +#define PGDIR_OFFSET(X) (((ulong)(X)) & (PGDIR_SIZE - 1))
> >  +
> > 
> > You have defined PGDIR_SIZE_L4_4K and PGDIR_MASK_L4_4K, but they
> > are not used in arm64.c:
> > 
> >   $ grep -e PGDIR_SIZE_L4_4K -e PGDIR_MASK_L4_4K arm64.c
> >   $
> 
> It is kinda copy-and-paste from L3_4K.
> PGDIR_MASK_L3_4K/PMD_SIZE_L3_4K/PMD_MASK_L3_4K are not used neither.
> 
> > Instead you define PGDIR_SIZE and PGDIR_MASK without the _L4_4K qualifiers,
> > and use them and PGDIR_OFFSET() in arm64.c.
> > 
> > Preferably convention should be followed such that the _L4_4K versions would
> > be used, but I see that PGDIR_SIZE_L4_4K is not equal to PGDIR_SIZE, and that
> > PGDIR_MASK_L4_4K is not equal to PGDIR_MASK.  What's going on there?
> 
> As you can see, those macros are used to calculate pgd_val and pud_base.
> I'd like to use the same formula as in the other level of tables,
> but the size and mask can be varied depending on a value of VA_BITS
> for 4-level translation.
> For 48-bit VA, luckily or not, PAGEOFFSET() would work instead of
> PGDIR_OFFSET(), and likewise machdep->pagemask instead of PGDIR_MASK,
> but we should not use them.
> That is why I define the macros as
>     #define PGDIR_SIZE  (1UL << ((48 - 39) + 3))
> 
> But I will agree that we'd better give them different names to avoid any confusion.
> Any suggestions?

I don't know -- maybe something with "PUD" in them since this is the
first time it's used?

Dave