Re: [PATCH] tcmu: Fix flushing cmd entry dcache page

[Mike Christie <mchristi@redhat.com>]

On 06/30/2017 03:14 AM, lixiubo@cmss.chinamobile.com wrote:
> From: Xiubo Li <lixiubo@cmss.chinamobile.com>
> 
> When feeding the tcmu's cmd ring, we need to flush the dcache page
> for the cmd entry to make sure these kernel stores are visible to
> user space mappings of that page.
> 
> For the none PAD cmd entry, this will be flushed at the end of the
> tcmu_queue_cmd_ring().
> 
> Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
> ---
>  drivers/target/target_core_user.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
> index 203bff1..930800c 100644
> --- a/drivers/target/target_core_user.c
> +++ b/drivers/target/target_core_user.c
> @@ -699,21 +699,21 @@ static inline size_t tcmu_cmd_get_cmd_size(struct tcmu_cmd *tcmu_cmd,
>  		size_t pad_size = head_to_end(cmd_head, udev->cmdr_size);
>  
>  		entry = (void *) mb + CMDR_OFF + cmd_head;
> -		tcmu_flush_dcache_range(entry, sizeof(*entry));


I think this patch looks ok. What was the reason for removing this and
the one at the bottom of the patch? Is it not needed because we are not
reading anything from the entry that could have been touched by userspace?

>  		tcmu_hdr_set_op(&entry->hdr.len_op, TCMU_OP_PAD);
>  		tcmu_hdr_set_len(&entry->hdr.len_op, pad_size);
>  		entry->hdr.cmd_id = 0; /* not used for PAD */
>  		entry->hdr.kflags = 0;
>  		entry->hdr.uflags = 0;
> +		tcmu_flush_dcache_range(entry, sizeof(*entry));
>  
>  		UPDATE_HEAD(mb->cmd_head, pad_size, udev->cmdr_size);
> +		tcmu_flush_dcache_range(mb, sizeof(*mb));
>  
>  		cmd_head = mb->cmd_head % udev->cmdr_size; /* UAM */
>  		WARN_ON(cmd_head != 0);
>  	}
>  
>  	entry = (void *) mb + CMDR_OFF + cmd_head;
> -	tcmu_flush_dcache_range(entry, sizeof(*entry));
>  	tcmu_hdr_set_op(&entry->hdr.len_op, TCMU_OP_CMD);
>  	entry->hdr.cmd_id = tcmu_cmd->cmd_id;
>  	entry->hdr.kflags = 0;
>