Re: [Xen-devel] Ping: [PATCH] fix off-by-one mistakes in vm_alloc()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/08/13 14:08, Jan Beulich wrote:
> Ping? (This is expected to fix recurring testsuite failures.)
>
>>>> On 18.07.13 at 11:59, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> Also add another pair of assertions to catch eventual further cases of
>> incorrect accounting, and remove the temporary debuggin messages again
>> which commit 68caac7f ("x86: don't use destroy_xen_mappings() for
>> vunmap()") added.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

(Tentatively, if I have followed the logic correctly)

Reviewed-by Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

>>
>> --- a/xen/common/vmap.c
>> +++ b/xen/common/vmap.c
>> @@ -57,8 +57,8 @@ void *vm_alloc(unsigned int nr, unsigned
>>      {
>>          struct page_info *pg;
>>  
>> -        ASSERT(!test_bit(vm_low, vm_bitmap));
>> -        for ( start = vm_low; ; )
>> +        ASSERT(vm_low == vm_top || !test_bit(vm_low, vm_bitmap));
>> +        for ( start = vm_low; start < vm_top; )
>>          {
>>              bit = find_next_bit(vm_bitmap, vm_top, start + 1);
>>              if ( bit > vm_top )
>> @@ -68,12 +68,18 @@ void *vm_alloc(unsigned int nr, unsigned
>>               * corresponding page a guard one.
>>               */
>>              start = (start + align) & ~(align - 1);
>> -            if ( start + nr <= bit )
>> -                break;
>> -            start = bit < vm_top ?
>> -                    find_next_zero_bit(vm_bitmap, vm_top, bit + 1) : bit;
>> -            if ( start >= vm_top )
>> -                break;
>> +            if ( bit < vm_top )
>> +            {
>> +                if ( start + nr < bit )
>> +                    break;
>> +                start = find_next_zero_bit(vm_bitmap, vm_top, bit + 1);
>> +            }
>> +            else
>> +            {
>> +                if ( start + nr <= bit )
>> +                    break;
>> +                start = bit;
>> +            }
>>          }
>>  
>>          if ( start < vm_top )
>> @@ -115,6 +121,10 @@ void *vm_alloc(unsigned int nr, unsigned
>>  
>>      for ( bit = start; bit < start + nr; ++bit )
>>          __set_bit(bit, vm_bitmap);
>> +    if ( bit < vm_top )
>> +        ASSERT(!test_bit(bit, vm_bitmap));
>> +    else
>> +        ASSERT(bit == vm_top);
>>      if ( start <= vm_low + 2 )
>>          vm_low = bit;
>>      spin_unlock(&vm_lock);
>> @@ -177,7 +187,6 @@ void *__vmap(const unsigned long *mfn, u
>>      void *va = vm_alloc(nr * granularity, align);
>>      unsigned long cur = (unsigned long)va;
>>  
>> -printk("vmap(%p:%#x)\n", va, nr * granularity);//temp
>>      for ( ; va && nr--; ++mfn, cur += PAGE_SIZE * granularity )
>>      {
>>          if ( map_pages_to_xen(cur, *mfn, granularity, flags) )
>> @@ -202,7 +211,6 @@ void vunmap(const void *va)
>>  
>>      destroy_xen_mappings(addr, addr + PAGE_SIZE * vm_size(va));
>>  #else /* Avoid tearing down intermediate page tables. */
>> -printk("vunmap(%p:%#x)\n", va, vm_size(va));//temp
>>      map_pages_to_xen((unsigned long)va, 0, vm_size(va), _PAGE_NONE);
>>  #endif
>>      vm_free(va);
>
>
>
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