On Thursday, April 24, 2014 1:02 AM, Steve Capper wrote: > On Fri, Apr 18, 2014 at 04:59:20PM +0900, Jungseok Lee wrote: > > This patch implements 4 levels of translation tables since 3 levels of > > page tables with 4KB pages cannot support 40-bit physical address > > space described in [1] due to the following issue. > > > > It is a restriction that kernel logical memory map with 4KB + 3 levels > > (0xffffffc000000000-0xffffffffffffffff) cannot cover RAM region from > > 544GB to 1024GB in [1]. Specifically, ARM64 kernel fails to create > > mapping for this region in map_mem function since __phys_to_virt for > > this region reaches to address overflow. > > > > If SoC design follows the document, [1], over 32GB RAM would be placed > > from 544GB. Even 64GB system is supposed to use the region from 544GB > > to 576GB for only 32GB RAM. Naturally, it would reach to enable 4 > > levels of page tables to avoid hacking __virt_to_phys and __phys_to_virt. > > > > However, it is recommended 4 levels of page table should be only > > enabled if memory map is too sparse or there is about 512GB RAM. > > Hello Jungseok, > A few comments can be found inline...
Hi Steve, The comments are very helpful. Thanks. [ ... ] > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index > > 0fd5650..f313a7a 100644 > > --- a/arch/arm64/kernel/head.S > > +++ b/arch/arm64/kernel/head.S > > @@ -37,8 +37,8 @@ > > > > /* > > * swapper_pg_dir is the virtual address of the initial page table. > > We place > > - * the page tables 3 * PAGE_SIZE below KERNEL_RAM_VADDR. The > > idmap_pg_dir has > > - * 2 pages and is placed below swapper_pg_dir. > > + * the page tables 4 * PAGE_SIZE below KERNEL_RAM_VADDR. The > > + idmap_pg_dir has > > + * 3 pages and is placed below swapper_pg_dir. > > */ > > #define KERNEL_RAM_VADDR (PAGE_OFFSET + TEXT_OFFSET) > > > > @@ -46,8 +46,8 @@ > > #error KERNEL_RAM_VADDR must start at 0xXXX80000 #endif > > > > -#define SWAPPER_DIR_SIZE (3 * PAGE_SIZE) > > -#define IDMAP_DIR_SIZE (2 * PAGE_SIZE) > > +#define SWAPPER_DIR_SIZE (4 * PAGE_SIZE) > > +#define IDMAP_DIR_SIZE (3 * PAGE_SIZE) > > > > .globl swapper_pg_dir > > .equ swapper_pg_dir, KERNEL_RAM_VADDR - SWAPPER_DIR_SIZE > > @@ -371,16 +371,29 @@ ENDPROC(__calc_phys_offset) > > > > /* > > * Macro to populate the PGD for the corresponding block entry in the > > next > > - * level (tbl) for the given virtual address. > > + * levels (tbl1 and tbl2) for the given virtual address. > > * > > - * Preserves: pgd, tbl, virt > > + * Preserves: pgd, tbl1, tbl2, virt > > tbl1 and tbl2 are *not* preserved for 4 level. tbl1 is bumped up one page to > make space for the pud, > then fed into create_block_mapping later. Your logic can be extended to 3 levels. In an original code, tbl is fed into create_block_mapping. That is why I've written them down as "preserves". I will fix it in the next version. > > * Corrupts: tmp1, tmp2 > > */ > > - .macro create_pgd_entry, pgd, tbl, virt, tmp1, tmp2 > > + .macro create_pgd_entry, pgd, tbl1, tbl2, virt, tmp1, tmp2 > > lsr \tmp1, \virt, #PGDIR_SHIFT > > and \tmp1, \tmp1, #PTRS_PER_PGD - 1 // PGD index > > - orr \tmp2, \tbl, #3 // PGD entry table type > > + orr \tmp2, \tbl1, #3 // PGD entry table type > > str \tmp2, [\pgd, \tmp1, lsl #3] > > +#ifdef CONFIG_ARM64_4_LEVELS > > + ldr \tbl2, =FIXADDR_TOP > > + cmp \tbl2, \virt > > Do we need this extra logic? See my other comment below where the fixed > mapping is placed down. > > > + add \tbl2, \tbl1, #PAGE_SIZE > > + b.ne 1f > > + add \tbl2, \tbl2, #PAGE_SIZE > > +1: > > + lsr \tmp1, \virt, #PUD_SHIFT > > + and \tmp1, \tmp1, #PTRS_PER_PUD - 1 // PUD index > > + orr \tmp2, \tbl2, #3 // PUD entry table type > > + str \tmp2, [\tbl1, \tmp1, lsl #3] > > + mov \tbl1, \tbl2 > > +#endif > > It may be easier to read to have a create_pud_entry macro too? Okay. I will write a create_pud_entry macro. > > .endm > > > > /* > > @@ -444,7 +457,7 @@ __create_page_tables: > > add x0, x25, #PAGE_SIZE // section table address > > ldr x3, =KERNEL_START > > add x3, x3, x28 // __pa(KERNEL_START) > > - create_pgd_entry x25, x0, x3, x5, x6 > > + create_pgd_entry x25, x0, x1, x3, x5, x6 > > ldr x6, =KERNEL_END > > mov x5, x3 // __pa(KERNEL_START) > > add x6, x6, x28 // __pa(KERNEL_END) > > @@ -455,7 +468,7 @@ __create_page_tables: > > */ > > add x0, x26, #PAGE_SIZE // section table address > > mov x5, #PAGE_OFFSET > > - create_pgd_entry x26, x0, x5, x3, x6 > > + create_pgd_entry x26, x0, x1, x5, x3, x6 > > ldr x6, =KERNEL_END > > mov x3, x24 // phys offset > > create_block_map x0, x7, x3, x5, x6 > > @@ -480,8 +493,11 @@ __create_page_tables: > > * Create the pgd entry for the fixed mappings. > > */ > > ldr x5, =FIXADDR_TOP // Fixed mapping virtual address > > - add x0, x26, #2 * PAGE_SIZE // section table address > > - create_pgd_entry x26, x0, x5, x6, x7 > > + add x0, x26, #PAGE_SIZE > > +#ifndef CONFIG_ARM64_4_LEVELS > > + add x0, x0, #PAGE_SIZE > > +#endif > > This is overly complicated. For <4 levels we set x0 to be: > ttbr1 + 2*PAGE_SIZE. For 4-levels, we set x0 to be ttbr1 + PAGE_SIZE, then > inside the create_pgd_entry > macro, we check the VA for FIXADDR_TOP then add another PAGE_SIZE. This is > presumably done so the same > PUD is used for the swapper block map and the FIXADDR map. > > If you assume that the PUD always follows the PGD for 4-levels, then you can > remove this #ifdef and > the conditional VA logic in set_pgd_entry. To make the logic simpler for <4 > levels, you could call > create_pud_entry in the middle of create_pgd_entry, then put down the actual > pgd after. Okay, I will revise it in an easy and neat way. > > + create_pgd_entry x26, x0, x1, x5, x6, x7 > > > > So before this patch we have the following created by > __create_page_tables: > > +========================+ <--- TEXT_OFFSET + PHYS_OFFSET > | FIXADDR (pmd or pte) | > +------------------------+ > | block map (pmd or pte) | > +------------------------+ > | PGDs for swapper | > +========================+ <--- TTBR1 swapper_pg_dir > | block map for idmap | > +------------------------+ > | PGDs for idmap | > +------------------------+ <--- TTBR0 idmap_pg_dir > > > After the patch, for 4 levels activated we have: > +========================+ <--- TEXT_OFFSET + PHYS_OFFSET > | FIXADDR (ptes) | > +------------------------+ > | block map (ptes) | > +------------------------+ > | PUDs for swapper | > +------------------------+ > | PGDs for swapper | > +========================+ <--- TTBR1 swapper_pg_dir > | block map for idmap | > +------------------------+ > | PUDs for idmap | > +------------------------+ > | PGDs for idmap | > +------------------------+ <--- TTBR0 idmap_pg_dir > > and without 4 levels activated we have: > +========================+ <--- TEXT_OFFSET + PHYS_OFFSET > | ZERO BYTES | > +------------------------+ > | FIXADDR (pmd or pte) | > +------------------------+ > | block map (pmd or pte) | > +------------------------+ > | PGDs for swapper | > +========================+ <--- TTBR1 swapper_pg_dir > | ZERO BYTES | > +------------------------+ > | block map for idmap | > +------------------------+ > | PGDs for idmap | > +------------------------+ <--- TTBR0 idmap_pg_dir > > This is a pity as we are potentially throwing away 128KB. > I would recommend only extending the sizes of IDMAP_DIR_SIZE and > SWAPPER_DIR_SIZE if necessary. Yes, you're right. I will introduce #ifdef statements for their size adjustment. Best Regards Jungseok Lee -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
