RE: [PATCH v3 2/6] Drivers: hv: vmbus: Reduce number of references to message in vmbus_on_msg_dpc()

[Michael Kelley]

From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Tuesday, December 8, 2020 11:08 PM
> 
> Simplify the function by removing various references to the hv_message
> 'msg', introduce local variables 'msgtype' and 'payload_size'.
> 
> Suggested-by: Juan Vazquez <juvazq@xxxxxxxxxxxxx>
> Suggested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
> Changes since v2:
>   - Squash patches #2 and #3
>   - Revisit commit message
> 
>  drivers/hv/vmbus_drv.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 502f8cd95f6d4..44bcf9ccdaf5f 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1057,9 +1057,11 @@ void vmbus_on_msg_dpc(unsigned long data)
>  	struct hv_message *msg = (struct hv_message *)page_addr +
>  				  VMBUS_MESSAGE_SINT;
>  	struct vmbus_channel_message_header *hdr;
> +	enum vmbus_channel_message_type msgtype;
>  	const struct vmbus_channel_message_table_entry *entry;
>  	struct onmessage_work_context *ctx;
>  	u32 message_type = msg->header.message_type;
> +	__u8 payload_size;
> 
>  	/*
>  	 * 'enum vmbus_channel_message_type' is supposed to always be 'u32' as
> @@ -1073,40 +1075,38 @@ void vmbus_on_msg_dpc(unsigned long data)
>  		return;
> 
>  	hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> +	msgtype = hdr->msgtype;
> 
>  	trace_vmbus_on_msg_dpc(hdr);
> 
> -	if (hdr->msgtype >= CHANNELMSG_COUNT) {
> -		WARN_ONCE(1, "unknown msgtype=%d\n", hdr->msgtype);
> +	if (msgtype >= CHANNELMSG_COUNT) {
> +		WARN_ONCE(1, "unknown msgtype=%d\n", msgtype);
>  		goto msg_handled;
>  	}
> 
> -	if (msg->header.payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
> -		WARN_ONCE(1, "payload size is too large (%d)\n",
> -			  msg->header.payload_size);
> +	payload_size = msg->header.payload_size;
> +	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
> +		WARN_ONCE(1, "payload size is too large (%d)\n", payload_size);
>  		goto msg_handled;
>  	}
> 
> -	entry = &channel_message_table[hdr->msgtype];
> +	entry = &channel_message_table[msgtype];
> 
>  	if (!entry->message_handler)
>  		goto msg_handled;
> 
> -	if (msg->header.payload_size < entry->min_payload_len) {
> -		WARN_ONCE(1, "message too short: msgtype=%d len=%d\n",
> -			  hdr->msgtype, msg->header.payload_size);
> +	if (payload_size < entry->min_payload_len) {
> +		WARN_ONCE(1, "message too short: msgtype=%d len=%d\n", msgtype,
> payload_size);
>  		goto msg_handled;
>  	}
> 
>  	if (entry->handler_type	== VMHT_BLOCKING) {
> -		ctx = kmalloc(sizeof(*ctx) + msg->header.payload_size,
> -			      GFP_ATOMIC);
> +		ctx = kmalloc(sizeof(*ctx) + payload_size, GFP_ATOMIC);
>  		if (ctx == NULL)
>  			return;
> 
>  		INIT_WORK(&ctx->work, vmbus_onmessage_work);
> -		memcpy(&ctx->msg, msg, sizeof(msg->header) +
> -		       msg->header.payload_size);
> +		memcpy(&ctx->msg, msg, sizeof(msg->header) + payload_size);
> 
>  		/*
>  		 * The host can generate a rescind message while we
> @@ -1115,7 +1115,7 @@ void vmbus_on_msg_dpc(unsigned long data)
>  		 * by offer_in_progress and by channel_mutex.  See also the
>  		 * inline comments in vmbus_onoffer_rescind().
>  		 */
> -		switch (hdr->msgtype) {
> +		switch (msgtype) {
>  		case CHANNELMSG_RESCIND_CHANNELOFFER:
>  			/*
>  			 * If we are handling the rescind message;
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>