From 36c51aac585ae467f3dd946ad44164df62dc8ac8 Mon Sep 17 00:00:00 2001
From: "Peter H. Froehlich" <peter.hans.froehlich@gmail.com>
Date: Sat, 10 Oct 2015 23:40:05 -0400
Subject: [PATCH] Check more kalloc()/mappages() failures, nits.

---
 vm.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/vm.c b/vm.c
index 5326d14..fc61781 100644
--- a/vm.c
+++ b/vm.c
@@ -8,8 +8,7 @@
 #include "elf.h"
 
 extern char data[];  // defined by kernel.ld
-pde_t *kpgdir;  // for use in scheduler()
-struct segdesc gdt[NSEGS];
+static pde_t *kpgdir;  // for use in scheduler()
 
 // Set up CPU's kernel segment descriptors.
 // Run once on entry on each CPU.
@@ -33,7 +32,7 @@ seginit(void)
 
   lgdt(c->gdt, sizeof(c->gdt));
   loadgs(SEG_KCPU << 3);
-  
+
   // Initialize cpu-local storage.
   cpu = c;
   proc = 0;
@@ -57,7 +56,7 @@ walkpgdir(pde_t *pgdir, const void *va, int alloc)
     // Make sure all those PTE_P bits are zero.
     memset(pgtab, 0, PGSIZE);
     // The permissions here are overly generous, but they can
-    // be further restricted by the permissions in the page table 
+    // be further restricted by the permissions in the page table
     // entries, if necessary.
     *pde = v2p(pgtab) | PTE_P | PTE_W | PTE_U;
   }
@@ -72,7 +71,7 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm)
 {
   char *a, *last;
   pte_t *pte;
-  
+
   a = (char*)PGROUNDDOWN((uint)va);
   last = (char*)PGROUNDDOWN(((uint)va) + size - 1);
   for(;;){
@@ -94,7 +93,7 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm)
 // current process's page table during system calls and interrupts;
 // page protection bits prevent user code from using the kernel's
 // mappings.
-// 
+//
 // setupkvm() and exec() set up every page table like this:
 //
 //   0..KERNBASE: user memory (text+data+stack+heap), mapped to
@@ -102,7 +101,7 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm)
 //   KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (for I/O space)
 //   KERNBASE+EXTMEM..data: mapped to EXTMEM..V2P(data)
 //                for the kernel's instructions and r/o data
-//   data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP, 
+//   data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP,
 //                                  rw data + free physical memory
 //   0xfe000000..0: mapped direct (devices such as ioapic)
 //
@@ -137,7 +136,7 @@ setupkvm(void)
   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, 
+    if(mappages(pgdir, k->virt, k->phys_end - k->phys_start,
                 (uint)k->phys_start, k->perm) < 0)
       return 0;
   return pgdir;
@@ -182,12 +181,14 @@ void
 inituvm(pde_t *pgdir, char *init, uint sz)
 {
   char *mem;
-  
+
   if(sz >= PGSIZE)
     panic("inituvm: more than a page");
-  mem = kalloc();
+  if ((mem = kalloc()) == 0)
+    panic("inituvm: cannot allocate memory");
   memset(mem, 0, PGSIZE);
-  mappages(pgdir, 0, PGSIZE, v2p(mem), PTE_W|PTE_U);
+  if (mappages(pgdir, 0, PGSIZE, v2p(mem), PTE_W|PTE_U) < 0)
+    panic("inituvm: cannot create pagetable");
   memmove(mem, init, sz);
 }
 
@@ -237,7 +238,8 @@ allocuvm(pde_t *pgdir, uint oldsz, uint newsz)
       return 0;
     }
     memset(mem, 0, PGSIZE);
-    mappages(pgdir, (char*)a, PGSIZE, v2p(mem), PTE_W|PTE_U);
+    if (mappages(pgdir, (char*)a, PGSIZE, v2p(mem), PTE_W|PTE_U) < 0)
+      panic("allocuvm: cannot create pagetable");
   }
   return newsz;
 }
-- 
2.50.1