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Kernel: Make the x86 paging code slightly less insane.

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Instead of PDE's and PTE's being weird wrappers around dword*, just have
MemoryManager::ensure_pte() return a PageDirectoryEntry&, which in turn has
a PageTableEntry* entries().

I've been trying to understand how things ended up this way, and I suspect
it was because I inadvertently invoked the PageDirectoryEntry copy ctor in
the original work on this, which must have made me very confused..

Anyways, now things are a bit saner and we can move forward towards a better
future, etc. :^)
This commit is contained in:
Andreas Kling 2019-06-26 21:45:56 +02:00
parent 0538adbabd
commit 183205d51c
4 changed files with 126 additions and 123 deletions
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105
Kernel/Arch/i386/CPU.h
View file

@ -1,11 +1,16 @@
#pragma once
#include <AK/Badge.h>
#include <AK/Noncopyable.h>
#include <Kernel/VirtualAddress.h>
#include <Kernel/kstdio.h>
#define PAGE_SIZE 4096
#define PAGE_MASK 0xfffff000
class MemoryManager;
class PageTableEntry;
struct [[gnu::packed]] TSS32
{
word backlink, __blh;
@ -79,6 +84,106 @@ union [[gnu::packed]] Descriptor
}
};
class PageDirectoryEntry {
AK_MAKE_NONCOPYABLE(PageDirectoryEntry);
public:
PageTableEntry* page_table_base() { return reinterpret_cast<PageTableEntry*>(m_raw & 0xfffff000u); }
void set_page_table_base(dword value)
{
m_raw &= 0xfff;
m_raw |= value & 0xfffff000;
}
dword raw() const { return m_raw; }
void copy_from(Badge<MemoryManager>, const PageDirectoryEntry& other) { m_raw = other.m_raw; }
enum Flags {
Present = 1 << 0,
ReadWrite = 1 << 1,
UserSupervisor = 1 << 2,
WriteThrough = 1 << 3,
CacheDisabled = 1 << 4,
};
bool is_present() const { return raw() & Present; }
void set_present(bool b) { set_bit(Present, b); }
bool is_user_allowed() const { return raw() & UserSupervisor; }
void set_user_allowed(bool b) { set_bit(UserSupervisor, b); }
bool is_writable() const { return raw() & ReadWrite; }
void set_writable(bool b) { set_bit(ReadWrite, b); }
bool is_write_through() const { return raw() & WriteThrough; }
void set_write_through(bool b) { set_bit(WriteThrough, b); }
bool is_cache_disabled() const { return raw() & CacheDisabled; }
void set_cache_disabled(bool b) { set_bit(CacheDisabled, b); }
void set_bit(byte bit, bool value)
{
if (value)
m_raw |= bit;
else
m_raw &= ~bit;
}
private:
dword m_raw;
};
class PageTableEntry {
AK_MAKE_NONCOPYABLE(PageTableEntry);
public:
void* physical_page_base() { return reinterpret_cast<void*>(m_raw & 0xfffff000u); }
void set_physical_page_base(dword value)
{
m_raw &= 0xfff;
m_raw |= value & 0xfffff000;
}
dword raw() const { return m_raw; }
enum Flags {
Present = 1 << 0,
ReadWrite = 1 << 1,
UserSupervisor = 1 << 2,
WriteThrough = 1 << 3,
CacheDisabled = 1 << 4,
};
bool is_present() const { return raw() & Present; }
void set_present(bool b) { set_bit(Present, b); }
bool is_user_allowed() const { return raw() & UserSupervisor; }
void set_user_allowed(bool b) { set_bit(UserSupervisor, b); }
bool is_writable() const { return raw() & ReadWrite; }
void set_writable(bool b) { set_bit(ReadWrite, b); }
bool is_write_through() const { return raw() & WriteThrough; }
void set_write_through(bool b) { set_bit(WriteThrough, b); }
bool is_cache_disabled() const { return raw() & CacheDisabled; }
void set_cache_disabled(bool b) { set_bit(CacheDisabled, b); }
void set_bit(byte bit, bool value)
{
if (value)
m_raw |= bit;
else
m_raw &= ~bit;
}
private:
dword m_raw;
};
static_assert(sizeof(PageDirectoryEntry) == 4);
static_assert(sizeof(PageTableEntry) == 4);
class IRQHandler;
void gdt_init();