From: Vijay Kumar <vijay.ac.kumar@xxxxxxxxxx> Date: Wed, 26 Jul 2017 14:57:01 -0500 > > On 7/26/2017 1:11 AM, David Miller wrote: >> From: Allen <allen.pais@xxxxxxxxxx> >> Date: Mon, 24 Jul 2017 19:33:27 +0530 >> >>>> This patch needs to go with sparc-5-Level-paging patch. I am still >>>> working on adding boot time selection option, so please ignore this >>>> patch for now. I will post this patch separately with sparc-5-level >>>> patch. >>> My bad. David, could you please ignore this patch for the moment. >> Wait, why do you need 5 level page tables for this? >> >> The existing 4 level code supports up to 53-bits and you need only 51 >> for M8. >> >> There is even a check for this limit in asm/pgtable_64.h: >> >> #if (MAX_PHYS_ADDRESS_BITS > PGDIR_SHIFT + PGDIR_BITS) >> #error MAX_PHYS_ADDRESS_BITS exceeds what kernel page tables can >> #support >> #endif >> >> #if (PGDIR_SHIFT + PGDIR_BITS) != 53 >> #error Page table parameters do not cover virtual address space >> #properly. >> #endif >> >> We've supported up to 53-bits forever, from page_64.h: >> >> #define MAX_PHYS_ADDRESS_BITS 53 > Issue is not with Physical-address-bits but with > virtual-address-bits. With this patch, virtual address bits for M8 is > increased to 54 whereas current pagetable supports up to 53 bits only. > > PGDIR_BITS + PUD_BITS + PMD_BITS + PAGE_SHIFT + PAGE_OFFSET = 10 + 10 > + 10 + 10 + 13 = 53 bits > > Just to verify, I applied this patch and M8 does not boot up. > > Did I miss anything? Ok, the chip can do 54 bits. Can you guys just live with 53 bits for now? Thanks. Please resubmit the M8 support patches, using 53 virtual address bits. You can add a comment there stating that the chip supports 54 but the 4-level page tables currently cannot support that. Maybe we can meanwhile figure out some trick to grab an extra virtual address bit from the page table layout without going to 5-levels. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
