Re: [patch v3] infiniband: uverbs: handle large number of entries

Jason Gunthorpe
2010-10-12T21:01:18Z

On Tue, Oct 12, 2010 at 01:31:17PM +0200, Dan Carpenter wrote:
> In the original code there was a potential integer overflow if you
> passed in a large cmd.ne. The calls to kmalloc() would allocate smaller
> buffers than intended, leading to memory corruption.

Keep in mind these are probably performance sensitive APIs, I was
imagining batching a small number and they copy_to_user ? No idea what
the various performance trades offs are..

> Please, please, check this. I've think I've done it right, but I don't
> have the hardware and can not test it.

Nor, do I.. I actually don't know what hardware uses this path? The
Mellanox cards use a user-space only version.

Maybe an iwarp card? I kinda recall some recent messages concerning
memory allocations in these paths for iwarp. I wonder if removing the
allocation is such a big win the larger number of copy_to_user calls
does not matter?

> It's strange to me that we return "in_len" on success.

Agree..

> +static int copy_header_to_user(void __user *dest, u32 count)
> +{
> + u32 header[2]; /* the second u32 is reserved */
> +
> + memset(header, 0, sizeof(header));

Don't you need header[0] = count ?

Maybe:
u32 header[2] = {count};

And let the compiler 0 the other word optimally. Also, I'm not matters
here, since you are zeroing user memory that isn't currently used..

> +static int copy_wc_to_user(void __user *dest, struct ib_wc *wc)
> +{
> + struct ib_uverbs_wc tmp;
> +
> + memset(&tmp, 0, sizeof(tmp));

I'd really like to see that memset go away for performance. Again
maybe use named initializers and let the compiler zero the
uninitialized (does it zero padding, I wonder?). Or pre-zero this
memory outside the loop..

Jason