From 9e4272c14e98dd702326ee46d8cda6b78708d9d0 Mon Sep 17 00:00:00 2001
From: Austin Clements <amdragon@mit.edu>
Date: Fri, 2 Sep 2011 14:34:29 -0400
Subject: [PATCH] Cleanup comments and fit setupkvm on same page as kmap, which
aligns lots of other things
---
vm.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/vm.c b/vm.c
index 3e217e1..c30694e 100644
--- a/vm.c
+++ b/vm.c
@@ -92,10 +92,9 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa,
// The mappings from logical to virtual are one to one (i.e.,
// segmentation doesn't do anything). There is one page table per
-// process, plus one that's used when a CPU is not running any
-// process (kpgdir). A user process uses the same page table as
-// the kernel; the page protection bits prevent it from using
-// anything other than its memory.
+// process, plus one that's used when a CPU is not running any process
+// (kpgdir). A user process uses the same page table as the kernel; the
+// page protection bits prevent it from accessing kernel memory.
//
// setupkvm() and exec() set up every page table like this:
// 0..KERNBASE: user memory (text+data+stack+heap), mapped to some free
@@ -108,10 +107,9 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa,
// 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 (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.
+// between KERNBASE+end and the end of physical memory (PHYSTOP).
+// The user program sits in the bottom of the address space, and the
+// kernel at the top at KERNBASE.
static struct kmap {
void *virt;
uint phys_start;
@@ -134,14 +132,12 @@ setupkvm(char* (*alloc)(void))
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)
return 0;
-
return pgdir;
}
--
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