pgtable.h

/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
 
/*
 * pgtable.h
 *
 *  PowerPC memory management structures
 *
 * It is a stripped down version of linux ppc file...
 *
 * Copyright (C) 1999  Eric Valette (eric.valette@free.fr)
 *                     Canon Centre Recherche France.
 *
 *  The license and distribution terms for this file may be
 *  found in the file LICENSE in this distribution or at
 *  http://www.rtems.org/license/LICENSE.
 */
 
#ifndef _LIBCPU_PGTABLE_H
#define _LIBCPU_PGTABLE_H
 
/*
 * The PowerPC MMU uses a hash table containing PTEs, together with
 * a set of 16 segment registers (on 32-bit implementations), to define
 * the virtual to physical address mapping.
 *
 * We use the hash table as an extended TLB, i.e. a cache of currently
 * active mappings.  We maintain a two-level page table tree, much like
 * that used by the i386, for the sake of the Linux memory management code.
 * Low-level assembler code in head.S (procedure hash_page) is responsible
 * for extracting ptes from the tree and putting them into the hash table
 * when necessary, and updating the accessed and modified bits in the
 * page table tree.
 *
 * The PowerPC MPC8xx uses a TLB with hardware assisted, software tablewalk.
 * We also use the two level tables, but we can put the real bits in them
 * needed for the TLB and tablewalk.  These definitions require Mx_CTR.PPM = 0,
 * Mx_CTR.PPCS = 0, and MD_CTR.TWAM = 1.  The level 2 descriptor has
 * additional page protection (when Mx_CTR.PPCS = 1) that allows TLB hit
 * based upon user/super access.  The TLB does not have accessed nor write
 * protect.  We assume that if the TLB get loaded with an entry it is
 * accessed, and overload the changed bit for write protect.  We use
 * two bits in the software pte that are supposed to be set to zero in
 * the TLB entry (24 and 25) for these indicators.  Although the level 1
 * descriptor contains the guarded and writethrough/copyback bits, we can
 * set these at the page level since they get copied from the Mx_TWC
 * register when the TLB entry is loaded.  We will use bit 27 for guard, since
 * that is where it exists in the MD_TWC, and bit 26 for writethrough.
 * These will get masked from the level 2 descriptor at TLB load time, and
 * copied to the MD_TWC before it gets loaded.
 */
 
/* PMD_SHIFT determines the size of the area mapped by the second-level page tables */
#define PMD_SHIFT   22
#define PMD_SIZE    (1UL << PMD_SHIFT)
#define PMD_MASK    (~(PMD_SIZE-1))
 
/* PGDIR_SHIFT determines what a third-level page table entry can map */
#define PGDIR_SHIFT 22
#define PGDIR_SIZE  (1UL << PGDIR_SHIFT)
#define PGDIR_MASK  (~(PGDIR_SIZE-1))
 
/*
 * entries per page directory level: our page-table tree is two-level, so
 * we don't really have any PMD directory.
 */
#define PTRS_PER_PTE    1024
#define PTRS_PER_PMD    1
#define PTRS_PER_PGD    1024
#define USER_PTRS_PER_PGD   (TASK_SIZE / PGDIR_SIZE)
 
/* Just any arbitrary offset to the start of the vmalloc VM area: the
 * current 64MB value just means that there will be a 64MB "hole" after the
 * physical memory until the kernel virtual memory starts.  That means that
 * any out-of-bounds memory accesses will hopefully be caught.
 * The vmalloc() routines leaves a hole of 4kB between each vmalloced
 * area for the same reason. ;)
 *
 * We no longer map larger than phys RAM with the BATs so we don't have
 * to worry about the VMALLOC_OFFSET causing problems.  We do have to worry
 * about clashes between our early calls to ioremap() that start growing down
 * from ioremap_base being run into the VM area allocations (growing upwards
 * from VMALLOC_START).  For this reason we have ioremap_bot to check when
 * we actually run into our mappings setup in the early boot with the VM
 * system.  This really does become a problem for machines with good amounts
 * of RAM.  -- Cort
 */
#define VMALLOC_OFFSET (0x4000000) /* 64M */
#define VMALLOC_START ((((long)high_memory + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1)))
#define VMALLOC_VMADDR(x) ((unsigned long)(x))
#define VMALLOC_END ioremap_bot
 
/*
 * Bits in a linux-style PTE.  These match the bits in the
 * (hardware-defined) PowerPC PTE as closely as possible.
 */
#define _PAGE_PRESENT   0x001   /* software: pte contains a translation */
#define _PAGE_USER  0x002   /* matches one of the PP bits */
#define _PAGE_RW    0x004   /* software: user write access allowed */
#define _PAGE_GUARDED   0x008
#define _PAGE_COHERENT  0x010   /* M: enforce memory coherence (SMP systems) */
#define _PAGE_NO_CACHE  0x020   /* I: cache inhibit */
#define _PAGE_WRITETHRU 0x040   /* W: cache write-through */
#define _PAGE_DIRTY 0x080   /* C: page changed */
#define _PAGE_ACCESSED  0x100   /* R: page referenced */
#define _PAGE_HWWRITE   0x200   /* software: _PAGE_RW & _PAGE_DIRTY */
#define _PAGE_SHARED    0
 
#define _PAGE_CHG_MASK  (PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
 
#define _PAGE_BASE  _PAGE_PRESENT | _PAGE_ACCESSED
#define _PAGE_WRENABLE  _PAGE_RW | _PAGE_DIRTY | _PAGE_HWWRITE
 
#define PAGE_NONE   __pgprot(_PAGE_PRESENT | _PAGE_ACCESSED)
 
#define PAGE_SHARED __pgprot(_PAGE_BASE | _PAGE_RW | _PAGE_USER | \
                 _PAGE_SHARED)
#define PAGE_COPY   __pgprot(_PAGE_BASE | _PAGE_USER)
#define PAGE_READONLY   __pgprot(_PAGE_BASE | _PAGE_USER)
#define PAGE_KERNEL __pgprot(_PAGE_BASE | _PAGE_WRENABLE | _PAGE_SHARED)
#define PAGE_KERNEL_CI  __pgprot(_PAGE_BASE | _PAGE_WRENABLE | _PAGE_SHARED | \
                 _PAGE_NO_CACHE )
 
/*
 * The PowerPC can only do execute protection on a segment (256MB) basis,
 * not on a page basis.  So we consider execute permission the same as read.
 * Also, write permissions imply read permissions.
 * This is the closest we can get..
 */
#define __P000  PAGE_NONE
#define __P001  PAGE_READONLY
#define __P010  PAGE_COPY
#define __P011  PAGE_COPY
#define __P100  PAGE_READONLY
#define __P101  PAGE_READONLY
#define __P110  PAGE_COPY
#define __P111  PAGE_COPY
 
#define __S000  PAGE_NONE
#define __S001  PAGE_READONLY
#define __S010  PAGE_SHARED
#define __S011  PAGE_SHARED
#define __S100  PAGE_READONLY
#define __S101  PAGE_READONLY
#define __S110  PAGE_SHARED
#define __S111  PAGE_SHARED
#endif /* _LIBCPU_PGTABLE_H */