Re: [PATCH] mm: add VM_STATIC flag to vmalloc and prevent from removing the areas

[Hoeun Ryu]

> On Apr 13, 2017, at 1:17 PM, Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> wrote:
> 
>> On 04/12/2017 10:31 AM, Hoeun Ryu wrote:
>> vm_area_add_early/vm_area_register_early() are used to reserve vmalloc area
>> during boot process and those virtually mapped areas are never unmapped.
>> So `OR` VM_STATIC flag to the areas in vmalloc_init() when importing
>> existing vmlist entries and prevent those areas from being removed from the
>> rbtree by accident.
> 
> I am wondering whether protection against accidental deletion
> of any vmap area should be done in remove_vm_area() function
> or the callers should take care of it. But I guess either way
> it works.
> 
>> 
>> Signed-off-by: Hoeun Ryu <hoeun.ryu@xxxxxxxxx>
>> ---
>> include/linux/vmalloc.h | 1 +
>> mm/vmalloc.c            | 9 ++++++---
>> 2 files changed, 7 insertions(+), 3 deletions(-)
>> 
>> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
>> index 46991ad..3df53fc 100644
>> --- a/include/linux/vmalloc.h
>> +++ b/include/linux/vmalloc.h
>> @@ -19,6 +19,7 @@ struct notifier_block;        /* in notifier.h */
>> #define VM_UNINITIALIZED    0x00000020    /* vm_struct is not fully initialized */
>> #define VM_NO_GUARD        0x00000040      /* don't add guard page */
>> #define VM_KASAN        0x00000080      /* has allocated kasan shadow memory */
>> +#define VM_STATIC        0x00000200
> 
> You might want to add some description in the comment saying
> its a sticky VM area which will never go away or something.
> 

OK. I will add some description.

>> /* bits [20..32] reserved for arch specific ioremap internals */
>> 
>> /*
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 8ef8ea1..fb5049a 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1262,7 +1262,7 @@ void __init vmalloc_init(void)
>>    /* Import existing vmlist entries. */
>>    for (tmp = vmlist; tmp; tmp = tmp->next) {
>>        va = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
>> -        va->flags = VM_VM_AREA;
>> +        va->flags = VM_VM_AREA | VM_STATIC;
>>        va->va_start = (unsigned long)tmp->addr;
>>        va->va_end = va->va_start + tmp->size;
>>        va->vm = tmp;
>> @@ -1480,7 +1480,7 @@ struct vm_struct *remove_vm_area(const void *addr)
>>    might_sleep();
>> 
>>    va = find_vmap_area((unsigned long)addr);
>> -    if (va && va->flags & VM_VM_AREA) {
>> +    if (va && va->flags & VM_VM_AREA && likely(!(va->flags & VM_STATIC))) {
> 
> 
> You might want to move the VM_STATIC check before the VM_VM_AREA
> check so in cases where the former is set we can save one more
> conditional check.
> 

OK, I'll fix this in the next version

Thank you for the review.