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Date: Mon, 28 Apr 2014 14:23:39 +0100 From: Steve Capper <steve.capper@...aro.org> To: Jungseok Lee <jays.lee@...sung.com> Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu, Catalin.Marinas@....com, 'Marc Zyngier' <Marc.Zyngier@....com>, 'Christoffer Dall' <christoffer.dall@...aro.org>, linux-kernel@...r.kernel.org, 'linux-samsung-soc' <linux-samsung-soc@...r.kernel.org>, sungjinn.chung@...sung.com, 'Arnd Bergmann' <arnd@...db.de>, kgene.kim@...sung.com, ilho215.lee@...sung.com Subject: Re: [PATCH v3 6/7] arm64: mm: Implement 4 levels of translation tables On Sun, Apr 27, 2014 at 12:37:35PM +0900, Jungseok Lee wrote: > 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 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. > > Is it too complicated to understand the logic? > > 1) For <4 levels: > PAGE_SIZE is added for FIXADDR map and x0 is passed to create pgd entry. > 2) For =4 levels: > PAGE_SIZE is added in the create_pgd_entry macro since FIXADDR map info > is needed to create pud entry. > > However, I agree that the code should be revised if other people feel > like it is a labyrinthine logic. > > > 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. > > create_pud_entry should distinguish block map from FIXADDR map although > PUD always follows the PGD in case of 4 levels. If we would like to avoid > unnecessary #ifdef, the conditional logic should be introduced in create_ > pgd_entry macro. > > I cannot find the "best" way even though I've tried to figure it out. > I would like to find out the most clear and self-descriptive expression. > > Could you give an idea on how to remove both conditional VA logic and #ifdef? Hello Jungseok, I had the following logic in my head: It compiles and runs on the model, but I've not tried it in anger. ========================================================================= .macro create_pud_entry, pgd, tbl, virt, pud, tmp1, tmp2 #ifdef CONFIG_ARM64_4_LEVELS add \tbl, \tbl, #PAGE_SIZE // bump tbl 1 page up. // to make room for pud add \pud, \pgd, #PAGE_SIZE // pgd points to pud which // follows pgd lsr \tmp1, \virt, #PUD_SHIFT and \tmp1, \tmp1, #PTRS_PER_PUD - 1 // PUD index orr \tmp2, \tbl, #3 // PUD entry table type str \tmp2, [\pud, \tmp1, lsl #3] #else mov \pud, \tbl // pgd points to section table // directly for < 4 levels #endif .endm /* * Macro to populate the PGD for the corresponding block entry in the next * level (tbl) for the given virtual address. * * Preserves: pgd, virt * Corrupts: tmp1, tmp2, tmp3 * Returns: tbl -> page where block mappings can be placed * (changed to make room for pud with 4levels, preserved otherwise) */ .macro create_pgd_entry, pgd, tbl, virt, tmp1, tmp2, tmp3 create_pud_entry \pgd, \tbl, \virt, \tmp3, \tmp1, \tmp2 lsr \tmp1, \virt, #PGDIR_SHIFT and \tmp1, \tmp1, #PTRS_PER_PGD - 1 // PGD index orr \tmp2, \tmp3, #3 // PGD entry table type str \tmp2, [\pgd, \tmp1, lsl #3] .endm ========================================================================= [Note I've changed the extra argument to create_pgd_entry to be at the end to make it easier to diff callers] So essentially, we bump up tbl if we are running with 4 levels of page table. We put the pgd down after the pud, and this allows us to sneak a pud in after the pgd if we need to, otherwise it points to the target for the section mapping. Does this work for you? (I go cross-eyed with too much assembler, so could have easily missed something). > > > > + 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 definitely helpful to understand head.S. > It would be good to add these figures to Documentation or comments. Please feel free to grab it if you want... :-). Otherwise, I can put a patch in for this, as I am working on some logic to remap the physical memory a PUD blocks for 4K granule. Cheers, -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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