/* Copyright (C) 2021,2022 fef <owo@fef.moe>.  All rights reserved. */

#pragma once
#ifndef _ARCH_PAGE_H_
#error "This file is not meant to be included directly, use <arch/page.h>"
#endif

/** @brief Binary logarithm of `HUGEPAGE_SIZE`. */
#define HUGEPAGE_SHIFT 22

#ifndef _ASM_SOURCE

#include <gay/cdefs.h>
#include <gay/types.h>

/**
 * @brief A single 32-bit Page Table Entry.
 * The layout matches that of the Intel SDM, vol 3, sect 4.3, fig 4-4.
 * Bits 9 and 10 (`slab` and `atomic`) are marked as AVL in the manual and
 * ignored by the MMU.  We only use them for `get_pflags()`/`set_pflags()`.
 */
struct x86_page_table_entry {
/*  0 */bool present:1;			/**< Page Fault on access if 0 */
/*  1 */bool rw:1;			/**< Page Fault on write if 0 */
/*  2 */bool user:1;			/**< Page Fault on user mode access if 0 */
/*  3 */bool write_through:1;		/**< Enable write-through caching */
/*  4 */bool cache_disabled:1;		/**< Disable caching in TLB */
/*  5 */bool accessed:1;		/**< 1 if page has been accessed */
/*  6 */bool dirty:1;			/**< 1 if page has been written to */
/*  7 */unsigned _reserved0:1;
/*  8 */bool global:1;			/**< Don't update the TLB on table swap if 1 */
/*  9 */bool slab:1;			/**< Used by the slab allocator */
/* 10 */bool atomic:1;			/**< Allocated atomically */
/* 11 */unsigned _unused:1;
/* 12 */uintptr_t shifted_address:20;	/**< Aligned pointer to the physical page */
} __packed;
#define __PFLAG_PRESENT		(1 << 0)
#define __PFLAG_RW		(1 << 1)
#define __PFLAG_USER		(1 << 2)
#define __PFLAG_WRITE_THROUGH	(1 << 3)
#define __PFLAG_NOCACHE		(1 << 4)
#define __PFLAG_ACCESSED	(1 << 5)
#define __PFLAG_DIRTY		(1 << 6)
#define __PFLAG_GLOBAL		(1 << 8)
#define __PFLAG_SLAB		(1 << 9)
#define __PFLAG_ATOMIC		(1 << 10)

struct x86_page_table {
	struct x86_page_table_entry entries[1024];
} __aligned(PAGE_SIZE);

/**
 * @brief Currently active page table at position `index` in the page directory.
 * The last entry in the page directory is mapped to itself, therefore being
 * interpreted by the MMU as a page table.  This has the effect that the last
 * page table, i.e. the page directory again, maps the entire page directory
 * structure so it can be manipulated while paging is active.  See the comment
 * at the beginning of `arch/x86/mm/page.c` for a more detailed explanation.
 *
 * @param index Table index in the page directory
 */
#define X86_CURRENT_PT(index) ( &((struct x86_page_table *)X86_PD_OFFSET)[index] )
#define X86_CURRENT_PTE(pd_index, pt_index) (&(X86_CURRENT_PT(pd_index)->entries[pt_index]))

struct x86_page_directory_entry {
/*  0 */bool present:1;		/**< Page Fault on access if 0 */
/*  1 */bool rw:1;		/**< Page Fault on write if 0 */
/*  2 */bool user:1;		/**< Page Fault on user mode access if 0 */
/*  3 */bool write_through:1;	/**< Enable write-through caching */
/*  4 */bool cache_disabled:1;	/**< Disable caching in TLB */
/*  5 */bool accessed:1;	/**< 1 if page has been accessed */
/*  6 */unsigned _reserved0:1;
/*  7 */bool huge:1;		/**< 0 = 4K, 1 = 4M */
/*  8 */unsigned _reserved1:1;
/*  9 */bool slab:1;		/**< Used by the slab allocator (only if `!huge`) */
/* 10 */bool atomic:1;		/**< Allocated atomically (only if `!huge`) */
/* 11 */unsigned _unused:1;
/* 12 */uintptr_t shifted_address:20;	/**< Aligned pointer to `struct x86_page_table` */
} __packed;
#define __PFLAG_HUGE		(1 << 7)

struct x86_page_directory {
	struct x86_page_directory_entry entries[1024];
} __aligned(PAGE_SIZE);

/**
 * @brief Currently active page directory.
 * The last entry in the page directory is mapped to itself, therefore being
 * interpreted by the MMU as a page table.  See the comment at the start of
 * `arch/x86/mm/page.c` for a more detailed explanation.
 */
#define X86_CURRENT_PD ((struct x86_page_directory *)X86_CURRENT_PT(1023))
#define X86_CURRENT_PDE(index) (&X86_CURRENT_PD->entries[index])

/**
 * @brief Arch dependent virtual memory information data structure (x86 version).
 * Outside of `/arch/x86`, this is treated as a completely obfuscated type,
 * and only pointers to it are stored and passed around.
 */
typedef struct x86_page_directory vm_info_t;

#endif /* not _ASM_SOURCE */