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/defs.h | 4 ++--
kernel/vm.c | 19 ++++++++++++++-----
2 files changed, 16 insertions(+), 7 deletions(-)
(limited to 'kernel')
diff --git a/kernel/defs.h b/kernel/defs.h
index 1c0b39a..bd89af0 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -185,9 +185,9 @@ pagetable_t uvmcreate(void);
void uvminit(pagetable_t, uchar *, uint);
uint64 uvmalloc(pagetable_t, uint64, uint64);
uint64 uvmdealloc(pagetable_t, uint64, uint64);
-int uvmcopy(pagetable_t, pagetable_t, uint64);
+int uvmcopy(pagetable_t, pagetable_t, uint64);
void uvmfree(pagetable_t, uint64);
-void mappages(pagetable_t, uint64, uint64, uint64, int);
+int mappages(pagetable_t, uint64, uint64, uint64, int);
void unmappages(pagetable_t, uint64, uint64, int);
uint64 walkaddr(pagetable_t, uint64);
int copyout(pagetable_t, uint64, char *, uint64);
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;
--
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