Ptab Class Reference

Public Types
enum	{   PRESENT = 1<<0 , RW = 1<<1 , USER = 1<<2 , ACCESS = 1<<5 ,   DIRTY = 1<<6 }
	Page attributes.

Static Public Member Functions
static bool	insert_mapping (mword virt, mword phys, mword attr)
	Inserts a 4 KB mapping into the page table. More...
static mword	get_mapping (mword virt)
	Returns the page table entry for the virtual address virt, INCLUDING THE ATTRIBUTE BITS. More...
static void *	remap (mword phys)
	Maps the passed physical address to the fixed virtual address REMAP_SADDR as a single 4MB page. More...

Member Function Documentation

get_mapping()

mword Ptab::get_mapping ( mword  virt )

static

Returns the page table entry for the virtual address virt, INCLUDING THE ATTRIBUTE BITS.

Get a page table entry corresponding to virtual address virt.

Returns

The requested page table entry.

{
    mword* pdir = static_cast<mword*>(Kalloc::phys2virt(Cpu::cr3()));
    mword* ptab;
 
    if ((pdir[virt >> 22] & PRESENT) == 0)
        return 0;
    else
        ptab = static_cast<mword*>(Kalloc::phys2virt (pdir[virt >> 22] & ~PAGE_MASK));
 
    return ptab[(virt >> PAGE_BITS) & 0x3ff];
}

insert_mapping()

bool Ptab::insert_mapping ( mword  virt, mword  phys, mword  attr  )

static

Inserts a 4 KB mapping into the page table.

Set a page table entry corresponding to virtual address virt to the combination of phys and attr.

Parameters

[in]	virt	Virtual address to be mapped.
[in]	phys	Physical address to map at virt.
[in]	attr	Page attributes such as PRESENT, RW, USER, ACCESS, DIRTY.

Returns

true in case of success, false otherwise.

{
    // load page directory virtual address
    mword* pdir = static_cast<mword*>(Kalloc::phys2virt(Cpu::cr3()));
    mword* ptab;
    // check if the required page table already exists
    if ((pdir[virt >> 22] & PRESENT) == 0) {
        // allocate a new page table
        ptab = static_cast<mword*>(Kalloc::allocator.alloc_page(1, Kalloc::FILL_0));
        if (!ptab)
            return false;
        mword p = Kalloc::virt2phys (ptab);
        // add the page table to page directory
        pdir[virt >> 22] = p | ACCESS | RW | PRESENT | USER;
    } else {
        // get the matching page table address
        ptab = static_cast<mword*>(Kalloc::phys2virt (pdir[virt >> 22] & ~PAGE_MASK));
    }
    assert ((phys & PAGE_MASK) == 0);
    // insert the requested mapping into the page table
    ptab[(virt >> PAGE_BITS) & 0x3ff] = (phys & ~PAGE_MASK) | (attr & PAGE_MASK);
    // flush TLB to update the cached mapping
    Cpu::flush();
    return true;
}

remap()

void * Ptab::remap ( mword  phys )

static

Maps the passed physical address to the fixed virtual address REMAP_SADDR as a single 4MB page.

This mapping is temporary, and is changed the next time this method is called.

This is useful for one-off reads from a given physical address. We cannot use Kalloc::phys2virt(), because the 1:1 mapping used by it may not cover the whole physical RAM.

{
    mword* pdir = static_cast<mword*>(Kalloc::phys2virt(Cpu::cr3()));
    // flush TLB : old 4M mapping
    // MK: why set 0 and flush here, why not flush after setting the real value?
    pdir[REMAP_SADDR >> 22] = 0;
    Cpu::flush(REMAP_SADDR);
    // insert new mapping
    // 0xffc... masks top 10 bits, 0xe3 sets page directory entry flags (0xe3 = 0b11100011)
    pdir[REMAP_SADDR >> 22] = (phys & 0xffc00000) + 0xe3;
    // 0x3f... masks bottom 22 bits
    return reinterpret_cast<void *>(REMAP_SADDR + (phys & 0x3fffff));
}

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The documentation for this class was generated from the following files:

• include/ptab.h
• src/ptab.cc