2475ff9d2c
This patch adds support for "earlyprintk=" parameter on the kernel command line. The format is: earlyprintk=<name>[,<addr>][,<options>] where <name> is the name of the (UART) device, e.g. "pl011", <addr> is the I/O address. The <options> aren't currently used. The mapping of the earlyprintk device is done very early during kernel boot and there are restrictions on which functions it can call. A special early_io_map() function is added which creates the mapping from the pre-defined EARLY_IOBASE to the device I/O address passed via the kernel parameter. The pgd entry corresponding to EARLY_IOBASE is pre-populated in head.S during kernel boot. Only PL011 is currently supported and it is assumed that the interface is already initialised by the boot loader before the kernel is started. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Arnd Bergmann <arnd@arndb.de>
76 lines
3.2 KiB
Plaintext
76 lines
3.2 KiB
Plaintext
Memory Layout on AArch64 Linux
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==============================
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Author: Catalin Marinas <catalin.marinas@arm.com>
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Date : 20 February 2012
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This document describes the virtual memory layout used by the AArch64
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Linux kernel. The architecture allows up to 4 levels of translation
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tables with a 4KB page size and up to 3 levels with a 64KB page size.
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AArch64 Linux uses 3 levels of translation tables with the 4KB page
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configuration, allowing 39-bit (512GB) virtual addresses for both user
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and kernel. With 64KB pages, only 2 levels of translation tables are
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used but the memory layout is the same.
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User addresses have bits 63:39 set to 0 while the kernel addresses have
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the same bits set to 1. TTBRx selection is given by bit 63 of the
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virtual address. The swapper_pg_dir contains only kernel (global)
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mappings while the user pgd contains only user (non-global) mappings.
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The swapper_pgd_dir address is written to TTBR1 and never written to
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TTBR0.
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AArch64 Linux memory layout:
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Start End Size Use
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-----------------------------------------------------------------------
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0000000000000000 0000007fffffffff 512GB user
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ffffff8000000000 ffffffbbfffeffff ~240GB vmalloc
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ffffffbbffff0000 ffffffbbffffffff 64KB [guard page]
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ffffffbc00000000 ffffffbdffffffff 8GB vmemmap
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ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap]
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ffffffbffbc00000 ffffffbffbdfffff 2MB earlyprintk device
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ffffffbffbe00000 ffffffbffbe0ffff 64KB PCI I/O space
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ffffffbbffff0000 ffffffbcffffffff ~2MB [guard]
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ffffffbffc000000 ffffffbfffffffff 64MB modules
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ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map
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Translation table lookup with 4KB pages:
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+--------+--------+--------+--------+--------+--------+--------+--------+
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|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
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+--------+--------+--------+--------+--------+--------+--------+--------+
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| | | | | |
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| | | | | v
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| | | | | [11:0] in-page offset
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| | | | +-> [20:12] L3 index
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| | | +-----------> [29:21] L2 index
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| | +---------------------> [38:30] L1 index
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| +-------------------------------> [47:39] L0 index (not used)
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+-------------------------------------------------> [63] TTBR0/1
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Translation table lookup with 64KB pages:
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+--------+--------+--------+--------+--------+--------+--------+--------+
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|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
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+--------+--------+--------+--------+--------+--------+--------+--------+
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| | | | |
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| | | | v
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| | | | [15:0] in-page offset
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| | | +----------> [28:16] L3 index
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| | +--------------------------> [41:29] L2 index (only 38:29 used)
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| +-------------------------------> [47:42] L1 index (not used)
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+-------------------------------------------------> [63] TTBR0/1
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