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

[Max Reitz]

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.

>     in this case @count may be not aligned. @start + @count

+are

With those fixed:

Reviewed-by: Max Reitz <address@hidden>

> + * 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);
>

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