From abfe9999f447c15d904b3c11f32d4a22a45470a0 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 1 Jul 2019 17:46:06 -0400
Subject: have fork() fail, not panic, if not enough phys mem

---
 kernel/vm.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

(limited to 'kernel/vm.c')

diff --git a/kernel/vm.c b/kernel/vm.c
index 580669f..7d67464 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -273,7 +273,9 @@ uvmfree(pagetable_t pagetable, uint64 sz)
 // its memory into a child's page table.
 // Copies both the page table and the
 // physical memory.
-void
+// returns 0 on success, -1 on failure.
+// frees any allocated pages on failure.
+int
 uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
 {
   pte_t *pte;
@@ -289,10 +291,15 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
     pa = PTE2PA(*pte);
     flags = PTE_FLAGS(*pte);
     if((mem = kalloc()) == 0)
-      panic("uvmcopy: kalloc failed");
+      goto err;
     memmove(mem, (char*)pa, PGSIZE);
     mappages(new, i, PGSIZE, (uint64)mem, flags);
   }
+  return 0;
+
+ err:
+  unmappages(new, 0, i, 1);
+  return -1;
 }
 
 // Copy from kernel to user.
-- 
cgit v1.2.3


From 1540c8b15ac35de9027e60804a786d23703d383d Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 11:04:35 -0400
Subject: COW tests

---
 kernel/vm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'kernel/vm.c')

diff --git a/kernel/vm.c b/kernel/vm.c
index 7d67464..d5ff594 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -97,8 +97,8 @@ walk(pagetable_t pagetable, uint64 va, int alloc)
 }
 
 // Look up a virtual address, return the physical address,
-// Can only be used to look up user pages.
 // or 0 if not mapped.
+// Can only be used to look up user pages.
 uint64
 walkaddr(pagetable_t pagetable, uint64 va)
 {
-- 
cgit v1.2.3


From f59c1bf1d82da4b445c1cff10c228ea55fa035d4 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 2 Jul 2019 11:45:06 -0400
Subject: try to continue from walk() failing to allocate a page-table page

---
 kernel/vm.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

(limited to 'kernel/vm.c')

diff --git a/kernel/vm.c b/kernel/vm.c
index d5ff594..bdb53c2 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -119,8 +119,9 @@ walkaddr(pagetable_t pagetable, uint64 va)
 
 // Create PTEs for virtual addresses starting at va that refer to
 // physical addresses starting at pa. va and size might not
-// be page-aligned.
-void
+// be page-aligned. Returns 0 on success, -1 if walk() couldn't
+// allocate a needed page-table page.
+int
 mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
 {
   uint64 a, last;
@@ -130,7 +131,7 @@ mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
   last = PGROUNDDOWN(va + size - 1);
   for(;;){
     if((pte = walk(pagetable, a, 1)) == 0)
-      panic("mappages: walk");
+      return -1;
     if(*pte & PTE_V)
       panic("remap");
     *pte = PA2PTE(pa) | perm | PTE_V;
@@ -139,6 +140,7 @@ mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
     a += PGSIZE;
     pa += PGSIZE;
   }
+  return 0;
 }
 
 // Remove mappings from a page table. The mappings in
@@ -222,7 +224,11 @@ uvmalloc(pagetable_t pagetable, uint64 oldsz, uint64 newsz)
       return 0;
     }
     memset(mem, 0, PGSIZE);
-    mappages(pagetable, a, PGSIZE, (uint64)mem, PTE_W|PTE_X|PTE_R|PTE_U);
+    if(mappages(pagetable, a, PGSIZE, (uint64)mem, PTE_W|PTE_X|PTE_R|PTE_U) != 0){
+      kfree(mem);
+      uvmdealloc(pagetable, a, oldsz);
+      return 0;
+    }
   }
   return newsz;
 }
@@ -293,7 +299,10 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
     if((mem = kalloc()) == 0)
       goto err;
     memmove(mem, (char*)pa, PGSIZE);
-    mappages(new, i, PGSIZE, (uint64)mem, flags);
+    if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){
+      kfree(mem);
+      goto err;
+    }
   }
   return 0;
 
-- 
cgit v1.2.3