mmu.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include	"all.h"
#include	"mem.h"
#include	"io.h"
#include	"ureg.h"

/*
 *  task state segment.  Plan 9 ignores all the task switching goo and just
 *  uses the tss for esp0 and ss0 on gate's into the kernel, interrupts,
 *  and exceptions.  The rest is completely ignored.
 *
 *  This means that we only need one tss in the whole system.
 */
typedef struct Tss	Tss;
struct Tss
{
	ulong	backlink;	/* unused */
	ulong	sp0;		/* pl0 stack pointer */
	ulong	ss0;		/* pl0 stack selector */
	ulong	sp1;		/* pl1 stack pointer */
	ulong	ss1;		/* pl1 stack selector */
	ulong	sp2;		/* pl2 stack pointer */
	ulong	ss2;		/* pl2 stack selector */
	ulong	cr3;		/* page table descriptor */
	ulong	eip;		/* instruction pointer */
	ulong	eflags;		/* processor flags */
	ulong	eax;		/* general (hah?) registers */
	ulong 	ecx;
	ulong	edx;
	ulong	ebx;
	ulong	esp;
	ulong	ebp;
	ulong	esi;
	ulong	edi;
	ulong	es;		/* segment selectors */
	ulong	cs;
	ulong	ss;
	ulong	ds;
	ulong	fs;
	ulong	gs;
	ulong	ldt;		/* local descriptor table */
	ulong	iomap;		/* io map base */
};
Tss tss;

/*
 *  segment descriptor initializers
 */
#define	DATASEGM(p) 	{ 0xFFFF, SEGG|SEGB|(0xF<<16)|SEGP|SEGPL(p)|SEGDATA|SEGW }
#define	EXECSEGM(p) 	{ 0xFFFF, SEGG|SEGD|(0xF<<16)|SEGP|SEGPL(p)|SEGEXEC|SEGR }
#define CALLGATE(s,o,p)	{ ((o)&0xFFFF)|((s)<<16), (o)&0xFFFF0000|SEGP|SEGPL(p)|SEGCG }
#define	D16SEGM(p) 	{ 0xFFFF, (0x0<<16)|SEGP|SEGPL(p)|SEGDATA|SEGW }
#define	E16SEGM(p) 	{ 0xFFFF, (0x0<<16)|SEGP|SEGPL(p)|SEGEXEC|SEGR }
#define	TSSSEGM(b,p)	{ ((b)<<16)|sizeof(Tss),\
			  ((b)&0xFF000000)|(((b)>>16)&0xFF)|SEGTSS|SEGPL(p)|SEGP }

/*
 *  global descriptor table describing all segments
 */
Segdesc gdt[] =
{
[NULLSEG]	{ 0, 0},		/* null descriptor */
[KDSEG]		DATASEGM(0),		/* kernel data/stack */
[KESEG]		EXECSEGM(0),		/* kernel code */
[UDSEG]		DATASEGM(3),		/* user data/stack */
[UESEG]		EXECSEGM(3),		/* user code */
[TSSSEG]	TSSSEGM(0,0),		/* tss segment */
};

static struct {
	ulong	va;
	ulong	pa;
} ktoppg;			/* prototype top level page table
				 * containing kernel mappings  */
static ulong	*kpt;		/* 2nd level page tables for kernel mem */

#define ROUNDUP(s,v)	(((s)+(v-1))&~(v-1))
/*
 *  offset of virtual address into
 *  top level page table
 */
#define TOPOFF(v)	(((ulong)(v))>>(2*PGSHIFT-2))

/*
 *  offset of virtual address into
 *  bottom level page table
 */
#define BTMOFF(v)	((((ulong)(v))>>(PGSHIFT))&(WD2PG-1))

/*
 *  Change current page table and the stack to use for exceptions
 *  (traps & interrupts).  The exception stack comes from the tss.
 *  Since we use only one tss, (we hope) there's no need for a
 *  puttr().
 */
static void
taskswitch(ulong pagetbl, ulong stack)
{
	tss.ss0 = KDSEL;
	tss.sp0 = stack;
tss.ss1 = KDSEL;
tss.sp1 = stack;
tss.ss2 = KDSEL;
tss.sp2 = stack;
	tss.cr3 = pagetbl;
	putcr3(pagetbl);
}

/*
 *  Create a prototype page map that maps all of memory into
 *  kernel (KZERO) space.  This is the default map.  It is used
 *  whenever the processor is not running a process or whenever running
 *  a process which does not yet have its own map.
 */
void
mmuinit(void)
{
	int i, nkpt, npage, nbytes;
	ulong x;
	ulong y;
	ulong *top;

	/*
	 *  set up the global descriptor table. we make the tss entry here
	 *  since it requires arithmetic on an address and hence cannot
	 *  be a compile or link time constant.
	 */
	x = (ulong)&tss;
	gdt[TSSSEG].d0 = (x<<16)|sizeof(Tss);
	gdt[TSSSEG].d1 = (x&0xFF000000)|((x>>16)&0xFF)|SEGTSS|SEGPL(0)|SEGP;
	putgdt(gdt, sizeof gdt);

	/*
	 *  set up system page tables.
	 *  map all of physical memory to start at KZERO.
	 *  leave a map entry for a user area.
	 */

	/*
	 *  allocate top level table
	 */
	top = ialloc(BY2PG, BY2PG);

	ktoppg.va = (ulong)top;
	ktoppg.pa = ktoppg.va & ~KZERO;

	/*  map all memory to KZERO */
	npage = mconf.topofmem/BY2PG;
	nbytes = PGROUND(npage*BY2WD);		/* words of page map */
	nkpt = nbytes/BY2PG;			/* pages of page map */

	kpt = ialloc(nbytes, BY2PG);

	for(i = 0; i < npage; i++)
		kpt[i] = (0+i*BY2PG) | PTEVALID | PTEKERNEL | PTEWRITE;
	x = TOPOFF(KZERO);
	y = ((ulong)kpt)&~KZERO;
	for(i = 0; i < nkpt; i++)
		top[x+i] = (y+i*BY2PG) | PTEVALID | PTEKERNEL | PTEWRITE;

	/*
	 *  set up the task segment
	 */
	memset(&tss, 0, sizeof(tss));
	taskswitch(ktoppg.pa, BY2PG + (ulong)m);
	puttr(TSSSEL);/**/
}

/*
 *  used to map a page into 16 meg - BY2PG for confinit(). tpt is the temporary
 *  page table set up by l.s.
 */
long*
mapaddr(ulong addr)
{
	ulong base;
	ulong off;
	static ulong *pte, top;
	extern ulong tpt[];

	if(pte == 0){
		top = (((ulong)tpt)+(BY2PG-1))&~(BY2PG-1);
		pte = (ulong*)top;
		top &= ~KZERO;
		top += BY2PG;
		pte += (4*1024*1024-BY2PG)>>PGSHIFT;
	}

	base = off = addr;
	base &= ~(KZERO|(BY2PG-1));
	off &= BY2PG-1;

	*pte = base|PTEVALID|PTEKERNEL|PTEWRITE; /**/
	putcr3((ulong)top);

	return (long*)(KZERO | 4*1024*1024-BY2PG | off);
}


#define PDX(va)		((((ulong)(va))>>22) & 0x03FF)
#define PTX(va)		((((ulong)(va))>>12) & 0x03FF)
#define PPN(x)		((x)&~(BY2PG-1))
#define KADDR(a)	((void*)((ulong)(a)|KZERO))

ulong*
mmuwalk(ulong* pdb, ulong va, int level, int create)
{
	ulong pa, *table;

	/*
	 * Walk the page-table pointed to by pdb and return a pointer
	 * to the entry for virtual address va at the requested level.
	 * If the entry is invalid and create isn't requested then bail
	 * out early. Otherwise, for the 2nd level walk, allocate a new
	 * page-table page and register it in the 1st level.
	 */
	table = &pdb[PDX(va)];
	if(!(*table & PTEVALID) && create == 0)
		return 0;

	switch(level){

	default:
		return 0;

	case 1:
		return table;

	case 2:
		if(*table & PTESIZE)
			panic("mmuwalk2: va 0x%ux entry 0x%ux\n", va, *table);
		if(!(*table & PTEVALID)){
			pa = PADDR(ialloc(BY2PG, BY2PG));
			*table = pa|PTEWRITE|PTEVALID;
		}
		table = KADDR(PPN(*table));

		return &table[PTX(va)];
	}
}

static Lock mmukmaplock;

ulong
mmukmap(ulong pa, ulong va, int size)
{
	ulong pae, *table, *pdb, pgsz, *pte, x;
	int pse, sync;
	extern int cpuidax, cpuiddx;

	pdb = (ulong*)ktoppg.va;
	if((cpuiddx & 0x08) && (getcr4() & 0x10))
		pse = 1;
	else
		pse = 0;
	sync = 0;

	pa = PPN(pa);
	if(va == 0)
		va = (ulong)KADDR(pa);
	else
		va = PPN(va);

	pae = pa + size;
	lock(&mmukmaplock);
	while(pa < pae){
		table = &pdb[PDX(va)];
		/*
		 * Possibly already mapped.
		 */
		if(*table & PTEVALID){
			if(*table & PTESIZE){
				/*
				 * Big page. Does it fit within?
				 * If it does, adjust pgsz so the correct end can be
				 * returned and get out.
				 * If not, adjust pgsz up to the next 4MB boundary
				 * and continue.
				 */
				x = PPN(*table);
				if(x != pa)
					panic("mmukmap1: pa 0x%ux  entry 0x%ux\n",
						pa, *table);
				x += 4*MB;
				if(pae <= x){
					pa = pae;
					break;
				}
				pgsz = x - pa;
				pa += pgsz;
				va += pgsz;

				continue;
			}
			else{
				/*
				 * Little page. Walk to the entry.
				 * If the entry is valid, set pgsz and continue.
				 * If not, make it so, set pgsz, sync and continue.
				 */
				pte = mmuwalk(pdb, va, 2, 0);
				if(pte && *pte & PTEVALID){
					x = PPN(*pte);
					if(x != pa)
						panic("mmukmap2: pa 0x%ux entry 0x%ux\n",
							pa, *pte);
					pgsz = BY2PG;
					pa += pgsz;
					va += pgsz;
					sync++;

					continue;
				}
			}
		}

		/*
		 * Not mapped. Check if it can be mapped using a big page -
		 * starts on a 4MB boundary, size >= 4MB and processor can do it.
		 * If not a big page, walk the walk, talk the talk.
		 * Sync is set.
		 */
		if(pse && (pa % (4*MB)) == 0 && (pae >= pa+4*MB)){
			*table = pa|PTESIZE|PTEWRITE|PTEUNCACHED|PTEVALID;
			pgsz = 4*MB;
		}
		else{
			pte = mmuwalk(pdb, va, 2, 1);
			*pte = pa|PTEWRITE|PTEUNCACHED|PTEVALID;
			pgsz = BY2PG;
		}
		pa += pgsz;
		va += pgsz;
		sync++;
	}
	unlock(&mmukmaplock);

	/*
	 * If something was added
	 * then need to sync up.
	 */
	if(sync)
		putcr3(ktoppg.pa);

	return pa;
}

ulong
upamalloc(ulong addr, int size, int align)
{
	ulong ae;

	/*
	 * Another horrible hack because
	 * I CAN'T BE BOTHERED WITH THIS FILESERVER BEING
	 * COMPLETELY INCOMPATIBLE ANYMORE.
	 */
	if((addr < mconf.topofmem) || align)
		panic("upamalloc: (0x%lux < 0x%lux) || %d\n",
			addr, mconf.topofmem, align);

	ae = mmukmap(addr, 0, size);

	/*
	 * Should check here that it was all delivered
	 * and put it back and barf if not.
	 */
	USED(ae);

	/*
	 * Be very careful this returns a PHYSICAL address.
	 */
	return addr;
}