From 6ddb762c7a7fe06096ccf344b7b15be4e035b0dd Mon Sep 17 00:00:00 2001
From: David Devecsery <ddevec@gatech.edu>
Date: Mon, 18 May 2020 13:35:48 -0400
Subject: [PATCH] Consolidated PHYSTOP operations, made it a little bit easier
 to define a dynamic phys_top

---
 kernel/include/defs.h |  4 ++--
 kernel/src/kalloc.c   | 11 +++++++++--
 kernel/src/main.c     |  4 ++--
 kernel/src/vm.c       | 21 ++++++++++++++++-----
 4 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/kernel/include/defs.h b/kernel/include/defs.h
index f1f20fd..85c8636 100644
--- a/kernel/include/defs.h
+++ b/kernel/include/defs.h
@@ -67,7 +67,7 @@ void            ioapicinit(void);
 char*           kalloc(void);
 void            kfree(char*);
 void            kinit1(void*, void*);
-void            kinit2(void*, void*);
+void            kinit2(void*, void*, uint);
 
 // kbd.c
 void            kbdintr(void);
@@ -163,7 +163,7 @@ void            uartputc(int);
 
 // vm.c
 void            seginit(void);
-void            kvmalloc(void);
+void            kvmalloc(uint);
 pde_t*          setupkvm(void);
 char*           uva2ka(pde_t*, char*);
 int             allocuvm(pde_t*, uint, uint);
diff --git a/kernel/src/kalloc.c b/kernel/src/kalloc.c
index 45f0aef..76c8f18 100644
--- a/kernel/src/kalloc.c
+++ b/kernel/src/kalloc.c
@@ -22,6 +22,8 @@ struct {
   struct spinlock lock;
   int use_lock;
   struct run *freelist;
+
+  uint phys_top;
 } kmem;
 
 // Initialization happens in two phases.
@@ -34,14 +36,17 @@ kinit1(void *vstart, void *vend)
 {
   initlock(&kmem.lock, "kmem");
   kmem.use_lock = 0;
+  // We haven't found phystop yet, don't use this.
+  kmem.phys_top = 0;
   freerange(vstart, vend);
 }
 
 void
-kinit2(void *vstart, void *vend)
+kinit2(void *vstart, void *vend, uint phys_top)
 {
   freerange(vstart, vend);
   kmem.use_lock = 1;
+  kmem.phys_top = phys_top;
 }
 
 void
@@ -62,8 +67,10 @@ kfree(char *v)
 {
   struct run *r;
 
-  if((uint)v % PGSIZE || v < end || V2P(v) >= PHYSTOP)
+  if((uint)v % PGSIZE || v < end || (kmem.phys_top && V2P(v) >= kmem.phys_top))
+  {
     panic("kfree");
+  }
 
   // Fill with junk to catch dangling refs.
   memset(v, 1, PGSIZE);
diff --git a/kernel/src/main.c b/kernel/src/main.c
index 6b6d639..30a5354 100644
--- a/kernel/src/main.c
+++ b/kernel/src/main.c
@@ -21,7 +21,7 @@ int
 main(void)
 {
   kinit1(end, P2V(4*1024*1024)); // phys page allocator
-  kvmalloc();      // kernel page table
+  kvmalloc(PHYSTOP); // kernel page table
   mpinit();        // detect other processors
   lapicinit();     // interrupt controller
   seginit();       // segment descriptors
@@ -35,7 +35,7 @@ main(void)
   fileinit();      // file table
   ideinit();       // disk 
   startothers();   // start other processors
-  kinit2(P2V(4*1024*1024), P2V(PHYSTOP)); // must come after startothers()
+  kinit2(P2V(4*1024*1024), P2V(PHYSTOP), PHYSTOP); // must come after startothers()
   userinit();      // first user process
   mpmain();        // finish this processor's setup
 }
diff --git a/kernel/src/vm.c b/kernel/src/vm.c
index ebebf64..a78e8b3 100644
--- a/kernel/src/vm.c
+++ b/kernel/src/vm.c
@@ -111,13 +111,16 @@ static struct kmap {
 } kmap[] = {
  { (void*)KERNBASE, 0,             EXTMEM,    PTE_W}, // I/O space
  { (void*)KERNLINK, V2P(KERNLINK), V2P(data), 0},     // kern text+rodata
- { (void*)data,     V2P(data),     PHYSTOP,   PTE_W}, // kern data+memory
+
+ // kern data+memory  -- the 0x5f.. addr should be the top of physical memory.  Fill that in dynamically in setupkvm.
+ { (void*)data,     V2P(data),     0x5F5F5F5F,   PTE_W},
+
  { (void*)DEVSPACE, DEVSPACE,      0,         PTE_W}, // more devices
 };
 
 // Set up kernel part of a page table.
 pde_t*
-setupkvm(void)
+setupkvm()
 {
   pde_t *pgdir;
   struct kmap *k;
@@ -125,22 +128,30 @@ setupkvm(void)
   if((pgdir = (pde_t*)kalloc()) == 0)
     return 0;
   memset(pgdir, 0, PGSIZE);
-  if (P2V(PHYSTOP) > (void*)DEVSPACE)
+  if (P2V(kmap[2].phys_end) > (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) < 0) {
+                (uint)k->phys_start, k->perm) < 0)
+    {
       freevm(pgdir);
       return 0;
     }
+  }
   return pgdir;
 }
 
 // Allocate one page table for the machine for the kernel address
 // space for scheduler processes.
 void
-kvmalloc(void)
+kvmalloc(uint phys_top)
 {
+  kmap[2].phys_end = phys_top;
+
   kpgdir = setupkvm();
   switchkvm();
 }
-- 
2.47.3