Big cleanup of LDT code. This code has very little type checking and is
not frequently used, so I audited the code, added type checking and size
optimizations to generate smaller assembly code. I changed the ldt count
to be in pages, and converted the char * ldt into a desc_struct.
Signed-off-by: Zachary Amsden <zach@vmware.com>
Index: linux-2.6.14-zach-work/arch/i386/kernel/ldt.c
==================================================================---
linux-2.6.14-zach-work.orig/arch/i386/kernel/ldt.c 2005-11-05 00:28:03.000000000
-0800
+++ linux-2.6.14-zach-work/arch/i386/kernel/ldt.c 2005-11-05 02:32:28.000000000
-0800
@@ -19,7 +19,7 @@
#include <asm/ldt.h>
#include <asm/desc.h>
-#ifdef CONFIG_SMP /* avoids "defined but not used" warnig */
+#ifdef CONFIG_SMP /* avoids "defined but not used" warning */
static void flush_ldt(void *null)
{
if (current->active_mm)
@@ -27,33 +27,33 @@ static void flush_ldt(void *null)
}
#endif
-static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
+static inline int alloc_ldt(mm_context_t *pc, const int old_pages, int
new_pages, const int reload)
{
- void *oldldt;
- void *newldt;
- int oldsize;
+ struct desc_struct *oldldt;
+ struct desc_struct *newldt;
- if (mincount <= pc->size)
- return 0;
- oldsize = pc->size;
- mincount = (mincount+511)&(~511);
- if (mincount*LDT_ENTRY_SIZE > PAGE_SIZE)
- newldt = vmalloc(mincount*LDT_ENTRY_SIZE);
+ if (new_pages > 1)
+ newldt = vmalloc(new_pages*PAGE_SIZE);
else
- newldt = kmalloc(mincount*LDT_ENTRY_SIZE, GFP_KERNEL);
+ newldt = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!newldt)
return -ENOMEM;
- if (oldsize)
- memcpy(newldt, pc->ldt, oldsize*LDT_ENTRY_SIZE);
+ if (old_pages)
+ memcpy(newldt, pc->ldt, old_pages*PAGE_SIZE);
oldldt = pc->ldt;
- memset(newldt+oldsize*LDT_ENTRY_SIZE, 0, (mincount-oldsize)*LDT_ENTRY_SIZE);
+ if (reload)
+ memset(newldt+old_pages*LDT_ENTRIES_PER_PAGE, 0,
(new_pages-old_pages)*PAGE_SIZE);
pc->ldt = newldt;
wmb();
- pc->size = mincount;
+ pc->ldt_pages = new_pages;
wmb();
+ /*
+ * If updating an active LDT, must reload LDT on all processors
+ * where it could be active.
+ */
if (reload) {
#ifdef CONFIG_SMP
cpumask_t mask;
@@ -67,8 +67,8 @@ static int alloc_ldt(mm_context_t *pc, i
load_LDT(pc);
#endif
}
- if (oldsize) {
- if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)
+ if (old_pages) {
+ if (old_pages > 1)
vfree(oldldt);
else
kfree(oldldt);
@@ -76,31 +76,43 @@ static int alloc_ldt(mm_context_t *pc, i
return 0;
}
-static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
+int copy_ldt(mm_context_t *new, mm_context_t *old)
{
- int err = alloc_ldt(new, old->size, 0);
- if (err < 0)
- return err;
- memcpy(new->ldt, old->ldt, old->size*LDT_ENTRY_SIZE);
- return 0;
+ int err;
+
+ down(&old->sem);
+ err = alloc_ldt(new, 0, old->ldt_pages, 0);
+ if (!err)
+ memcpy(new->ldt, old->ldt, old->ldt_pages*PAGE_SIZE);
+ up(&old->sem);
+ return err;
+}
+
+void destroy_ldt(mm_context_t *pc)
+{
+ int pages = pc->ldt_pages;
+ struct desc_struct *ldt = pc->ldt;
+
+ if (pc == ¤t->active_mm->context)
+ clear_LDT();
+ if (pages > 1)
+ vfree(ldt);
+ else
+ kfree(ldt);
+ pc->ldt_pages = 0;
+ pc->ldt = NULL;
}
-/*
- * we do not have to muck with descriptors here, that is
- * done in switch_mm() as needed.
- */
int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
struct mm_struct * old_mm;
int retval = 0;
+ memset(&mm->context, 0, sizeof(mm->context));
init_MUTEX(&mm->context.sem);
- mm->context.size = 0;
old_mm = current->mm;
- if (old_mm && old_mm->context.size > 0) {
- down(&old_mm->context.sem);
+ if (old_mm && unlikely(old_mm->context.ldt)) {
retval = copy_ldt(&mm->context, &old_mm->context);
- up(&old_mm->context.sem);
}
return retval;
}
@@ -110,37 +122,30 @@ int init_new_context(struct task_struct
*/
void destroy_context(struct mm_struct *mm)
{
- if (mm->context.size) {
- if (mm == current->active_mm)
- clear_LDT();
- if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
- vfree(mm->context.ldt);
- else
- kfree(mm->context.ldt);
- mm->context.size = 0;
- }
+ if (unlikely(mm->context.ldt))
+ destroy_ldt(&mm->context);
}
static int read_ldt(void __user * ptr, unsigned long bytecount)
{
int err;
unsigned long size;
- struct mm_struct * mm = current->mm;
+ mm_context_t *pc = ¤t->mm->context;
- if (!mm->context.size)
+ if (!pc->ldt_pages)
return 0;
if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
- down(&mm->context.sem);
- size = mm->context.size*LDT_ENTRY_SIZE;
+ down(&pc->sem);
+ size = pc->ldt_pages*PAGE_SIZE;
if (size > bytecount)
size = bytecount;
err = 0;
- if (copy_to_user(ptr, mm->context.ldt, size))
+ if (copy_to_user(ptr, pc->ldt, size))
err = -EFAULT;
- up(&mm->context.sem);
+ up(&pc->sem);
if (err < 0)
goto error_return;
if (size != bytecount) {
@@ -176,10 +181,11 @@ static int read_default_ldt(void __user
static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode)
{
- struct mm_struct * mm = current->mm;
+ mm_context_t *pc = ¤t->mm->context;
__u32 entry_1, entry_2;
int error;
struct user_desc ldt_info;
+ int page_number;
error = -EINVAL;
if (bytecount != sizeof(ldt_info))
@@ -198,9 +204,11 @@ static int write_ldt(void __user * ptr,
goto out;
}
- down(&mm->context.sem);
- if (ldt_info.entry_number >= mm->context.size) {
- error = alloc_ldt(¤t->mm->context, ldt_info.entry_number+1,
1);
+ page_number = ldt_info.entry_number / LDT_ENTRIES_PER_PAGE;
+ down(&pc->sem);
+ if (page_number >= pc->ldt_pages) {
+ error = alloc_ldt(pc, pc->ldt_pages,
+ page_number+1, 1);
if (error < 0)
goto out_unlock;
}
@@ -221,11 +229,11 @@ static int write_ldt(void __user * ptr,
/* Install the new entry ... */
install:
- write_ldt_entry(mm->context.ldt, ldt_info.entry_number, entry_1, entry_2);
+ write_ldt_entry(pc->ldt, ldt_info.entry_number, entry_1, entry_2);
error = 0;
out_unlock:
- up(&mm->context.sem);
+ up(&pc->sem);
out:
return error;
}
Index: linux-2.6.14-zach-work/include/asm-i386/desc.h
==================================================================---
linux-2.6.14-zach-work.orig/include/asm-i386/desc.h 2005-11-05
01:26:46.000000000 -0800
+++ linux-2.6.14-zach-work/include/asm-i386/desc.h 2005-11-05 02:30:35.000000000
-0800
@@ -218,7 +218,7 @@ static inline void clear_LDT(void)
static inline void load_LDT_nolock(mm_context_t *pc, int cpu)
{
void *segments = pc->ldt;
- int count = pc->size;
+ int count = pc->ldt_pages * LDT_ENTRIES_PER_PAGE;
if (likely(!count)) {
segments = &default_ldt[0];
Index: linux-2.6.14-zach-work/include/asm-i386/mmu.h
==================================================================---
linux-2.6.14-zach-work.orig/include/asm-i386/mmu.h 2005-11-05 00:28:03.000000000
-0800
+++ linux-2.6.14-zach-work/include/asm-i386/mmu.h 2005-11-05 01:34:31.000000000
-0800
@@ -9,9 +9,9 @@
* cpu_vm_mask is used to optimize ldt flushing.
*/
typedef struct {
- int size;
struct semaphore sem;
- void *ldt;
+ struct desc_struct *ldt;
+ int ldt_pages;
} mm_context_t;
#endif
