Re: [PATCH v2 01/11] dirtylimit: Fix overflow when computing MB

[Markus Armbruster]

huang...@chinatelecom.cn writes:

> From: Hyman Huang(黄勇) 
>
> overity points out a overflow problem when computing MB,

Coverity

> dirty_ring_size and TARGET_PAGE_SIZE are both 32 bits,
> multiplication will be done as a 32-bit operation, which
> could overflow. Simplify the formula.
>
> Meanwhile, fix spelling mistake of variable name.
>
> Reported-by: Peter Maydell 
> Signed-off-by: Peter Maydell 
> Signed-off-by: Richard Henderson 
> Signed-off-by: Hyman Huang(黄勇) 

Re: [PATCH v2 01/11] dirtylimit: Fix overflow when computing MB

[Peter Xu]

On Mon, Nov 21, 2022 at 11:26:33AM -0500, huang...@chinatelecom.cn 
wrote:
> From: Hyman Huang(黄勇) 
> 
> overity points out a overflow problem when computing MB,
> dirty_ring_size and TARGET_PAGE_SIZE are both 32 bits,
> multiplication will be done as a 32-bit operation, which
> could overflow. Simplify the formula.
> 
> Meanwhile, fix spelling mistake of variable name.
> 
> Reported-by: Peter Maydell 
> Signed-off-by: Peter Maydell 
> Signed-off-by: Richard Henderson 
> Signed-off-by: Hyman Huang(黄勇) 

Reviewed-by: Peter Xu 

-- 
Peter Xu

[PATCH v2 01/11] dirtylimit: Fix overflow when computing MB

[huangy81]

From: Hyman Huang(黄勇) 

overity points out a overflow problem when computing MB,
dirty_ring_size and TARGET_PAGE_SIZE are both 32 bits,
multiplication will be done as a 32-bit operation, which
could overflow. Simplify the formula.

Meanwhile, fix spelling mistake of variable name.

Reported-by: Peter Maydell 
Signed-off-by: Peter Maydell 
Signed-off-by: Richard Henderson 
Signed-off-by: Hyman Huang(黄勇) 
---
 softmmu/dirtylimit.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/softmmu/dirtylimit.c b/softmmu/dirtylimit.c
index 1266855..940d238 100644
--- a/softmmu/dirtylimit.c
+++ b/softmmu/dirtylimit.c
@@ -236,14 +236,14 @@ static inline int64_t 
dirtylimit_dirty_ring_full_time(uint64_t dirtyrate)
 {
 static uint64_t max_dirtyrate;
 uint32_t dirty_ring_size = kvm_dirty_ring_size();
-uint64_t dirty_ring_size_meory_MB =
-dirty_ring_size * TARGET_PAGE_SIZE >> 20;
+uint32_t dirty_ring_size_memory_MB =
+dirty_ring_size >> (20 - TARGET_PAGE_BITS);
 
 if (max_dirtyrate < dirtyrate) {
 max_dirtyrate = dirtyrate;
 }
 
-return dirty_ring_size_meory_MB * 100 / max_dirtyrate;
+return dirty_ring_size_memory_MB * 100ULL / max_dirtyrate;
 }
 
 static inline bool dirtylimit_done(uint64_t quota,
-- 
1.8.3.1