sanchayanmaity/xv6-cs450
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Switch back to #define for PHYSTOP. Using the E820 to retrieve the memory map is too complicated (must be done in 16-bit real-mode, probably enlarged bootblock beyond 512 bytes, and a #define requires less explanation).

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This commit is contained in:
Frans Kaashoek 2011-08-16 20:23:17 -04:00
parent c3dcf47966
commit 5f069dcf2f
3 changed files with 8 additions and 14 deletions
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5
kalloc.c
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@ -19,7 +19,6 @@ struct {
} kmem;
extern char end[]; // first address after kernel loaded from ELF file
extern uint maxpa; // Maximum physical address
static char *newend;
// simple page allocator to get off the ground during entry
@ -51,7 +50,7 @@ kinit(void)
initlock(&kmem.lock, "kmem");
p = (char*)PGROUNDUP((uint)newend);
for(; p + PGSIZE <= (char*)p2v(maxpa); p += PGSIZE)
for(; p + PGSIZE <= (char*)p2v(PHYSTOP); p += PGSIZE)
kfree(p);
}
@ -65,7 +64,7 @@ kfree(char *v)
{
struct run *r;
if((uint)v % PGSIZE || v < end || v2p(v) >= maxpa)
if((uint)v % PGSIZE || v < end || v2p(v) >= PHYSTOP)
panic("kfree");
// Fill with junk to catch dangling refs.

1
memlayout.h
View file

@ -1,6 +1,7 @@
// Memory layout
#define EXTMEM 0x100000 // Start of extended memory
#define PHYSTOP 0xE000000 // Top physical memory (too hard to get from E820)
#define DEVSPACE 0xFE000000 // Other devices are at high addresses
// Key addresses for address space layout (see kmap in vm.c for the layout)

16
vm.c
View file

@ -8,7 +8,6 @@
#include "elf.h"
extern char data[]; // defined in data.S
uint maxpa; // max physical address
pde_t *kpgdir; // for use in scheduler()
struct segdesc gdt[NSEGS];
@ -103,11 +102,11 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm, char* (*alloc)(vo
// 0..USERTOP : user memory (text, data, stack, heap), mapped to some unused phys mem
// KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (below extended memory)
// KERNBASE+EXTMEM..KERNBASE+end : mapped to EXTMEM..end (mapped without write permission)
// KERNBASE+end..KERBASE+maxpa : mapped to end..maxpa (rw data + free memory)
// KERNBASE+end..KERBASE+PHYSTOP : mapped to end..PHYSTOP (rw data + free memory)
// 0xfe000000..0 : mapped direct (devices such as ioapic)
//
// The kernel allocates memory for its heap and for user memory
// between kernend and the end of physical memory (maxpa).
// between kernend and the end of physical memory (PHYSTOP).
// The virtual address space of each user program includes the kernel
// (which is inaccessible in user mode). The user program sits in
// the bottom of the address space, and the kernel at the top at KERNBASE.
@ -119,7 +118,7 @@ static struct kmap {
} kmap[] = {
{ P2V(0), 0, 1024*1024, PTE_W}, // First 1Mbyte contains BIOS and some IO devices
{ (void *)KERNLINK, V2P(KERNLINK), V2P(data), 0}, // kernel text, rodata
{ data, V2P(data), 0, PTE_W}, // kernel data, memory
{ data, V2P(data), PHYSTOP, PTE_W}, // kernel data, memory
{ (void*)DEVSPACE, DEVSPACE, 0, PTE_W}, // more devices
};
@ -130,17 +129,12 @@ setupkvm(char* (*alloc)(void))
pde_t *pgdir;
struct kmap *k;
if (kmap[2].phys_end == 0) {
maxpa = detect_memory();
kmap[2].phys_end = maxpa;
if (p2v(maxpa) > kmap[3].virt)
panic("detect_memory: too much memory");
}
if((pgdir = (pde_t*)alloc()) == 0)
return 0;
memset(pgdir, 0, PGSIZE);
k = kmap;
if (p2v(PHYSTOP) > (void *) DEVSPACE)
panic("PHYSTOP too high");
for(k = kmap; k < &kmap[NELEM(kmap)]; k++)
if(mappages(pgdir, k->virt, k->phys_end - k->phys_start, (uint)k->phys_start,
k->perm, alloc) < 0)