Re: [PATCH 3/6] i386 virtualization - Make ldt a desc struct

[Zachary Amsden <zach@vmware.com>]

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Chuck Ebbert wrote:

>
>>@@ -97,14 +96,16 @@
>> 
>> void destroy_ldt(struct mm_struct *mm)
>> {
>>+     int pages = mm->context.ldt_pages;
>>+
>>      if (mm == current->active_mm)
>>              clear_LDT();
>>-     ClearPagesLDT(mm->context.ldt, (mm->context.size * LDT_ENTRY_SIZE) / PAGE_SIZE);
>>-     if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
>>+     ClearPagesLDT(mm->context.ldt, pages);
>>+     if (pages > 1)
>>              vfree(mm->context.ldt);
>>      else
>>              kfree(mm->context.ldt);
>>-     mm->context.size = 0;
>>+     mm->context.ldt_pages = 0;   <====================
>> }
>> 
>> static int read_ldt(void __user * ptr, unsigned long bytecount)
>>    
>>
>
>  destroy_ldt does not zero "ldt", just the size.  Potential bug?
>  
>

Not a bug, truly unnecessary at all.


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Several reviewers noticed that initialization and destruction of the
mm->context is unnecessary, since the entire MM struct is zeroed on
allocation anyways.

Verified with BUG_ON(mm->context.ldt || mm->context.ldt_pages);

Signed-off-by: Zachary Amsden <zach@vmware.com>
Index: linux-2.6.13/include/asm-i386/mmu_context.h
===================================================================
--- linux-2.6.13.orig/include/asm-i386/mmu_context.h	2005-08-15 11:23:32.000000000 -0700
+++ linux-2.6.13/include/asm-i386/mmu_context.h	2005-08-16 11:35:11.000000000 -0700
@@ -16,7 +16,6 @@
 	struct mm_struct * old_mm;
 	int retval = 0;
 
-	memset(&mm->context, 0, sizeof(mm->context));
 	init_MUTEX(&mm->context.sem);
 	old_mm = current->mm;
 	if (old_mm && unlikely(old_mm->context.ldt)) {
Index: linux-2.6.13/arch/i386/kernel/ldt.c
===================================================================
--- linux-2.6.13.orig/arch/i386/kernel/ldt.c	2005-08-15 11:23:32.000000000 -0700
+++ linux-2.6.13/arch/i386/kernel/ldt.c	2005-08-16 11:12:59.000000000 -0700
@@ -105,7 +105,6 @@
 		vfree(mm->context.ldt);
 	else
 		kfree(mm->context.ldt);
-	mm->context.ldt_pages = 0;
 }
 
 static int read_ldt(void __user * ptr, unsigned long bytecount)