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-rw-r--r--kernel/defs.h2
-rw-r--r--kernel/memlayout.h3
-rw-r--r--kernel/proc.c18
-rw-r--r--kernel/proc.h2
-rw-r--r--kernel/trap.c2
-rw-r--r--kernel/virtio_disk.c2
-rw-r--r--kernel/vm.c59
7 files changed, 46 insertions, 42 deletions
diff --git a/kernel/defs.h b/kernel/defs.h
index 2d8f85b..2b082a3 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -193,7 +193,7 @@ uint64 walkaddr(pagetable_t, uint64);
int copyout(pagetable_t, uint64, char *, uint64);
int copyin(pagetable_t, char *, uint64, uint64);
int copyinstr(pagetable_t, char *, uint64, uint64);
-char* mapkstack(uint64);
+void kmap(uint64, uint64, uint64, int);
uint64 kernelpa(uint64);
void clearpteu(pagetable_t, uint64);
diff --git a/kernel/memlayout.h b/kernel/memlayout.h
index c15e398..ace0464 100644
--- a/kernel/memlayout.h
+++ b/kernel/memlayout.h
@@ -53,6 +53,9 @@
// map the trampoline page to the highest address,
// in both user and kernel space.
#define TRAMPOLINE (MAXVA - PGSIZE)
+
+// map kernel stacks beneath the trampoline,
+// each surrounded by invalid guard pages.
#define KSTACK(p) (TRAMPOLINE - ((p)+1)* 2*PGSIZE)
// User memory layout.
diff --git a/kernel/proc.c b/kernel/proc.c
index cebef1a..5ce31c7 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -28,12 +28,18 @@ procinit(void)
initlock(&pid_lock, "nextpid");
for(p = proc; p < &proc[NPROC]; p++) {
initlock(&p->lock, "proc");
- // Allocate a page for the kernel stack.
- uint64 kstack = KSTACK((int) (p - proc));
- if((p->kstack = mapkstack(kstack)) == 0) {
- panic("procinit");
- }
+
+ // Allocate a page for the process's kernel stack.
+ // Map it high in memory, followed by an invalid
+ // guard page.
+ char *pa = kalloc();
+ if(pa == 0)
+ panic("kalloc");
+ uint64 va = KSTACK((int) (p - proc));
+ kmap(va, (uint64)pa, PGSIZE, PTE_R | PTE_W);
+ p->kstack = va;
}
+ kvminithart();
}
// Must be called with interrupts disabled,
@@ -113,7 +119,7 @@ found:
// which returns to user space.
memset(&p->context, 0, sizeof p->context);
p->context.ra = (uint64)forkret;
- p->context.sp = (uint64)p->kstack + PGSIZE;
+ p->context.sp = p->kstack + PGSIZE;
return p;
}
diff --git a/kernel/proc.h b/kernel/proc.h
index 8f94d30..0b358aa 100644
--- a/kernel/proc.h
+++ b/kernel/proc.h
@@ -96,7 +96,7 @@ struct proc {
int pid; // Process ID
// these are private to the process, so p->lock need not be held.
- char *kstack; // Bottom of kernel stack for this process
+ uint64 kstack; // Bottom of kernel stack for this process
uint64 sz; // Size of process memory (bytes)
pagetable_t pagetable; // Page table
struct trapframe *tf; // data page for trampoline.S
diff --git a/kernel/trap.c b/kernel/trap.c
index 1af7c00..a41301a 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -101,7 +101,7 @@ usertrapret(void)
// set up values that trampoline.S will need when
// the process next re-enters the kernel.
p->tf->kernel_satp = r_satp();
- p->tf->kernel_sp = (uint64)p->kstack + PGSIZE;
+ p->tf->kernel_sp = p->kstack + PGSIZE;
p->tf->kernel_trap = (uint64)usertrap;
p->tf->kernel_hartid = r_tp();
diff --git a/kernel/virtio_disk.c b/kernel/virtio_disk.c
index 6620037..3406478 100644
--- a/kernel/virtio_disk.c
+++ b/kernel/virtio_disk.c
@@ -199,6 +199,8 @@ virtio_disk_rw(struct buf *b)
buf0.reserved = 0;
buf0.sector = sector;
+ // buf0 is on a kernel stack, which is not direct mapped,
+ // thus the call to kernelpa().
desc[idx[0]].addr = (uint64) kernelpa((uint64) &buf0);
desc[idx[0]].len = sizeof(buf0);
desc[idx[0]].flags = VRING_DESC_F_NEXT;
diff --git a/kernel/vm.c b/kernel/vm.c
index 7dc84ba..b327b94 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -27,33 +27,26 @@ kvminit()
memset(kernel_pagetable, 0, PGSIZE);
// uart registers
- mappages(kernel_pagetable, UART0, PGSIZE,
- UART0, PTE_R | PTE_W);
+ kmap(UART0, UART0, PGSIZE, PTE_R | PTE_W);
// virtio mmio disk interface
- mappages(kernel_pagetable, VIRTIO0, PGSIZE,
- VIRTIO0, PTE_R | PTE_W);
+ kmap(VIRTIO0, VIRTIO0, PGSIZE, PTE_R | PTE_W);
// CLINT
- mappages(kernel_pagetable, CLINT, 0x10000,
- CLINT, PTE_R | PTE_W);
+ kmap(CLINT, CLINT, 0x10000, PTE_R | PTE_W);
// PLIC
- mappages(kernel_pagetable, PLIC, 0x4000000,
- PLIC, PTE_R | PTE_W);
+ kmap(PLIC, PLIC, 0x400000, PTE_R | PTE_W);
// map kernel text executable and read-only.
- mappages(kernel_pagetable, KERNBASE, (uint64)etext-KERNBASE,
- KERNBASE, PTE_R | PTE_X);
+ kmap(KERNBASE, KERNBASE, (uint64)etext-KERNBASE, PTE_R | PTE_X);
// map kernel data and the physical RAM we'll make use of.
- mappages(kernel_pagetable, (uint64)etext, PHYSTOP-(uint64)etext,
- (uint64)etext, PTE_R | PTE_W);
+ kmap((uint64)etext, (uint64)etext, PHYSTOP-(uint64)etext, PTE_R | PTE_W);
// map the trampoline for trap entry/exit to
// the highest virtual address in the kernel.
- mappages(kernel_pagetable, TRAMPOLINE, PGSIZE,
- (uint64)trampout, PTE_R | PTE_X);
+ kmap(TRAMPOLINE, (uint64)trampout, PGSIZE, PTE_R | PTE_X);
}
// Switch h/w page table register to the kernel's page table,
@@ -117,6 +110,15 @@ walkaddr(pagetable_t pagetable, uint64 va)
return pa;
}
+// add a mapping to the kernel page table.
+// only used when booting.
+// does not flush TLB or enable paging.
+void
+kmap(uint64 va, uint64 pa, uint64 sz, int perm)
+{
+ if(mappages(kernel_pagetable, va, sz, pa, perm) != 0)
+ panic("kmap");
+}
// Create PTEs for virtual addresses starting at va that refer to
// physical addresses starting at pa. va and size might not
@@ -405,25 +407,13 @@ copyinstr(pagetable_t pagetable, char *dst, uint64 srcva, uint64 max)
}
}
-char *
-mapkstack(uint64 kstack)
-{
- char *k = kalloc();
- if(k == 0) {
- return 0;
- }
- if (mappages(kernel_pagetable, kstack, PGSIZE,
- (uint64) k, PTE_R | PTE_W) == 0) {
- kvminithart();
- return (char *) kstack;
- }
- kfree(k);
- return 0;
-}
-
-// assumes va is page aligned
+// translate a kernel virtual address to
+// a physical address. only needed for
+// addresses on the stack.
+// assumes va is page aligned.
uint64
-kernelpa(uint64 va) {
+kernelpa(uint64 va)
+{
uint64 off = va % PGSIZE;
pte_t *pte;
uint64 pa;
@@ -437,8 +427,11 @@ kernelpa(uint64 va) {
return pa+off;
}
+// mark a PTE invalid for user access.
+// used by exec for the user stack guard page.
void
-clearpteu(pagetable_t pagetable, uint64 va) {
+clearpteu(pagetable_t pagetable, uint64 va)
+{
pte_t *pte;
pte = walk(pagetable, va, 0);
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