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

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?