Problem statement:
"compressed data are not fully copied to destination buffer when compressed data size is greater than source data"
Why:
5th argument of crypto_comp_compress function is *dlen, which tell the compression driver how many bytes the destination buffer space is allocated (allowed to write data).
This *dlen is important especially for H/W accelerator based compression driver because it is dangerous if we allow the H/W accelerator to access memory beyond *dst + *dlen.
Note that buffer location would be passed as physical address.
Due to the above reason, H/W accelerator based compression driver need to honor *dlen value when it serves crypto_comp_compress API.
Today, we pass slen = PAGE_SIZE and *dlen=PAGE_SIZE to crypto_comp_compress in zswap.c.
If compressed data size is greater than source (uncompressed) data size, H/W accelerator cannot copy (deliver) the entire compressed data.
Thank you,
Taeil
On 9/18/18, 7:15 AM, "Dan Streetman" <ddstreet@xxxxxxxx> wrote:
On Mon, Sep 17, 2018 at 7:10 PM Um, Taeil <taeilum@xxxxxxxxxx> wrote:
>
> Currently, we allocate PAGE_SIZE * 2 for zswap_dstmem which is used as compression destination buffer.
>
> However, we pass only half of the size (PAGE_SIZE) to crypto_comp_compress.
>
> This might not be a problem for CPU based existing lzo, lz4 crypto compression driver implantation.
>
> However, this could be a problem for some H/W acceleration compression drivers, which honor destination buffer size when it prepares H/W resources.
How exactly could it be a problem?
>
> Actually, this patch is aligned with what zram is passing when it calls crypto_comp_compress.
>
> The following simple patch will solve this problem. I tested it with existing crypto/lzo.c and crypto/lz4.c compression driver and it works fine.
>
>
>
>
>
> --- mm/zswap.c.orig 2018-09-14 14:36:37.984199232 -0700
>
> +++ mm/zswap.c 2018-09-14 14:36:53.340189681 -0700
>
> @@ -1001,7 +1001,7 @@ static int zswap_frontswap_store(unsigne
>
> struct zswap_entry *entry, *dupentry;
>
> struct crypto_comp *tfm;
>
> int ret;
>
> - unsigned int hlen, dlen = PAGE_SIZE;
>
> + unsigned int hlen, dlen = PAGE_SIZE * 2;
>
> unsigned long handle, value;
>
> char *buf;
>
> u8 *src, *dst;
>
>
>
>
>
>
>
> Thank you,
>
> Taeil
>
>
