Re: [Qemu-devel] [PATCH 1/7] XBZRLE: Fix one XBZRLE corruption issues

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Gonglei (Arei) (arei.gonglei@huawei.com) wrote:
> The page may not be inserted into cache after executing save_xbzrle_page.
> In case of failure to insert, the original page should be sent rather
> than the page in the cache.
> 
> Signed-off-by: ChenLiang <chenliang88@huawei.com>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>

Nice catch.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  arch_init.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index fe17279..bc8d0eb 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -303,7 +303,7 @@ static void xbzrle_cache_zero_page(ram_addr_t current_addr)
>  
>  #define ENCODING_FLAG_XBZRLE 0x1
>  
> -static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
> +static int save_xbzrle_page(QEMUFile *f, uint8_t **current_data,
>                              ram_addr_t current_addr, RAMBlock *block,
>                              ram_addr_t offset, int cont, bool last_stage)
>  {
> @@ -311,19 +311,23 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
>      uint8_t *prev_cached_page;
>  
>      if (!cache_is_cached(XBZRLE.cache, current_addr)) {
> +        acct_info.xbzrle_cache_miss++;
>          if (!last_stage) {
> -            if (cache_insert(XBZRLE.cache, current_addr, current_data) == -1) {
> +            if (cache_insert(XBZRLE.cache, current_addr, *current_data) == -1) {
>                  return -1;
> +            } else {
> +                /* update *current_data when the page has been
> +                   inserted into cache */
> +                *current_data = get_cached_data(XBZRLE.cache, current_addr);
>              }
>          }
> -        acct_info.xbzrle_cache_miss++;
>          return -1;
>      }
>  
>      prev_cached_page = get_cached_data(XBZRLE.cache, current_addr);
>  
>      /* save current buffer into memory */
> -    memcpy(XBZRLE.current_buf, current_data, TARGET_PAGE_SIZE);
> +    memcpy(XBZRLE.current_buf, *current_data, TARGET_PAGE_SIZE);
>  
>      /* XBZRLE encoding (if there is no overflow) */
>      encoded_len = xbzrle_encode_buffer(prev_cached_page, XBZRLE.current_buf,
> @@ -336,7 +340,10 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
>          DPRINTF("Overflow\n");
>          acct_info.xbzrle_overflows++;
>          /* update data in the cache */
> -        memcpy(prev_cached_page, current_data, TARGET_PAGE_SIZE);
> +        if (!last_stage) {
> +            memcpy(prev_cached_page, *current_data, TARGET_PAGE_SIZE);
> +            *current_data = prev_cached_page;
> +        }
>          return -1;
>      }
>  
> @@ -559,15 +566,9 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
>                   */
>                  xbzrle_cache_zero_page(current_addr);
>              } else if (!ram_bulk_stage && migrate_use_xbzrle()) {
> -                bytes_sent = save_xbzrle_page(f, p, current_addr, block,
> +                bytes_sent = save_xbzrle_page(f, &p, current_addr, block,
>                                                offset, cont, last_stage);
>                  if (!last_stage) {
> -                    /* We must send exactly what's in the xbzrle cache
> -                     * even if the page wasn't xbzrle compressed, so that
> -                     * it's right next time.
> -                     */
> -                    p = get_cached_data(XBZRLE.cache, current_addr);
> -
>                      /* Can't send this cached data async, since the cache page
>                       * might get updated before it gets to the wire
>                       */
> -- 
> 1.7.12.4
> 
> Best regards,
> -Gonglei
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK