Re: [Qemu-devel] [PATCH v2] util/hbitmap: strict hbitmap_reset

[Vladimir Sementsov-Ogievskiy]

06.08.2019 19:09, Max Reitz wrote:
> On 06.08.19 17:26, Vladimir Sementsov-Ogievskiy wrote:
>> hbitmap_reset has an unobvious property: it rounds requested region up.
>> It may provoke bugs, like in recently fixed write-blocking mode of
>> mirror: user calls reset on unaligned region, not keeping in mind that
>> there are possible unrelated dirty bytes, covered by rounded-up region
>> and information of this unrelated "dirtiness" will be lost.
>>
>> Make hbitmap_reset strict: assert that arguments are aligned, allowing
>> only one exception when @start + @count == hb->orig_size. It's needed
>> to comfort users of hbitmap_next_dirty_area, which cares about
>> hb->orig_size.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>> ---
>>
>> v2 based on Max's https://github.com/XanClic/qemu.git block
>> which will be merged soon to 4.1, and this patch goes to 4.2
>> Based-on: https://github.com/XanClic/qemu.git block
>>
>> v1 was "[PATCH] util/hbitmap: fix unaligned reset", and as I understand
>> we all agreed to just assert alignment instead of aligning down
>> automatically.
>>
>>   include/qemu/hbitmap.h | 5 +++++
>>   tests/test-hbitmap.c   | 2 +-
>>   util/hbitmap.c         | 4 ++++
>>   3 files changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
>> index 4afbe6292e..7865e819ca 100644
>> --- a/include/qemu/hbitmap.h
>> +++ b/include/qemu/hbitmap.h
>> @@ -132,6 +132,11 @@ void hbitmap_set(HBitmap *hb, uint64_t start, uint64_t 
>> count);
>>    * @count: Number of bits to reset.
>>    *
>>    * Reset a consecutive range of bits in an HBitmap.
>> + * @start and @count must be aligned to bitmap granularity. The only 
>> exception
>> + * is resetting the tail of the bitmap: @count may be equal to @start +
>> + * hb->orig_size,
> 
> s/@start + hb->orig_size/hb->orig_size - @start/, I think.

Ha, I wanted to say start + count equal to orig_size. Yours is OK too of course.

> 
>>      in this case @count may be not aligned. @start + @count
> 
> +are
> 
> With those fixed:
> 
> Reviewed-by: Max Reitz <address@hidden>

Thanks!

> 
>> + * allowed to be greater than hb->orig_size, but only if @start < 
>> hb->orig_size
>> + * and @start + @count = ALIGN_UP(hb->orig_size, granularity).
>>    */
>>   void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count);
>>   
>> diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
>> index 592d8219db..2be56d1597 100644
>> --- a/tests/test-hbitmap.c
>> +++ b/tests/test-hbitmap.c
>> @@ -423,7 +423,7 @@ static void test_hbitmap_granularity(TestHBitmapData 
>> *data,
>>       hbitmap_test_check(data, 0);
>>       hbitmap_test_set(data, 0, 3);
>>       g_assert_cmpint(hbitmap_count(data->hb), ==, 4);
>> -    hbitmap_test_reset(data, 0, 1);
>> +    hbitmap_test_reset(data, 0, 2);
>>       g_assert_cmpint(hbitmap_count(data->hb), ==, 2);
>>   }
>>   
>> diff --git a/util/hbitmap.c b/util/hbitmap.c
>> index bcc0acdc6a..586920cb52 100644
>> --- a/util/hbitmap.c
>> +++ b/util/hbitmap.c
>> @@ -476,6 +476,10 @@ void hbitmap_reset(HBitmap *hb, uint64_t start, 
>> uint64_t count)
>>       /* Compute range in the last layer.  */
>>       uint64_t first;
>>       uint64_t last = start + count - 1;
>> +    uint64_t gran = 1ULL << hb->granularity;
>> +
>> +    assert(!(start & (gran - 1)));
>> +    assert(!(count & (gran - 1)) || (start + count == hb->orig_size));
>>   
>>       trace_hbitmap_reset(hb, start, count,
>>                           start >> hb->granularity, last >> hb->granularity);
>>
> 
> 


-- 
Best regards,
Vladimir