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Date: Tue, 29 Apr 2014 13:12:27 +0900 From: Jungseok Lee <jays.lee@...sung.com> To: 'Steve Capper' <steve.capper@...aro.org> 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 Monday, April 28, 2014 10:24 PM, Steve Capper wrote: > 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. Hello Steve, It works well as both host and guest on the model. > ========================================================================= > > .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). It is a better description compared to my logic. I fully understand your intention now. It would be good to adopt your code instead of mine. How about participating as an author of this part if you are okay? I am posting v4 patches as soon as possible and then figuring out a way to take you as an author of this head.S. > > > > > > + 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. It is better to write a patch by you, not me. Then, I will review it. Best Regards Jungseok Lee -- 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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