RE: [PATCH 4/6] Drivers: hv: vmbus: Introduce vmbus_request_addr_match()

[Michael Kelley (LINUX)]

From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Wednesday, April 6, 2022 9:30 PM
> 
> The function can be used to retrieve and clear/remove a transation ID
> from a channel requestor, provided the memory address corresponding to
> the ID equals a specified address.  The function, and its 'lockless'
> variant __vmbus_request_addr_match(), will be used by hv_pci.
> 
> Refactor vmbus_request_addr() to reuse the 'newly' introduced code.
> 
> No functional change.
> 
> Suggested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
>  drivers/hv/channel.c   | 65 ++++++++++++++++++++++++++++++------------
>  include/linux/hyperv.h |  5 ++++
>  2 files changed, 52 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> index 585a8084848bf..49f10a603a091 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -1279,17 +1279,11 @@ u64 vmbus_next_request_id(struct vmbus_channel
> *channel, u64 rqst_addr)
>  }
>  EXPORT_SYMBOL_GPL(vmbus_next_request_id);
> 
> -/*
> - * vmbus_request_addr - Returns the memory address stored at @trans_id
> - * in @rqstor. Uses a spin lock to avoid race conditions.
> - * @channel: Pointer to the VMbus channel struct
> - * @trans_id: Request id sent back from Hyper-V. Becomes the requestor's
> - * next request id.
> - */
> -u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id)
> +/* As in vmbus_request_addr_match() but without the requestor lock */
> +u64 __vmbus_request_addr_match(struct vmbus_channel *channel, u64 trans_id,
> +			       u64 rqst_addr)
>  {
>  	struct vmbus_requestor *rqstor = &channel->requestor;
> -	unsigned long flags;
>  	u64 req_addr;
> 
>  	/* Check rqstor has been initialized */
> @@ -1300,25 +1294,60 @@ u64 vmbus_request_addr(struct vmbus_channel
> *channel, u64 trans_id)
>  	if (!trans_id)
>  		return VMBUS_RQST_ERROR;
> 
> -	spin_lock_irqsave(&rqstor->req_lock, flags);
> -
>  	/* Data corresponding to trans_id is stored at trans_id - 1 */
>  	trans_id--;
> 
>  	/* Invalid trans_id */
> -	if (trans_id >= rqstor->size || !test_bit(trans_id, rqstor->req_bitmap)) {
> -		spin_unlock_irqrestore(&rqstor->req_lock, flags);
> +	if (trans_id >= rqstor->size || !test_bit(trans_id, rqstor->req_bitmap))
>  		return VMBUS_RQST_ERROR;
> -	}
> 
>  	req_addr = rqstor->req_arr[trans_id];
> -	rqstor->req_arr[trans_id] = rqstor->next_request_id;
> -	rqstor->next_request_id = trans_id;
> +	if (rqst_addr == VMBUS_RQST_ADDR_ANY || req_addr == rqst_addr) {
> +		rqstor->req_arr[trans_id] = rqstor->next_request_id;
> +		rqstor->next_request_id = trans_id;
> 
> -	/* The already held spin lock provides atomicity */
> -	bitmap_clear(rqstor->req_bitmap, trans_id, 1);
> +		/* The already held spin lock provides atomicity */
> +		bitmap_clear(rqstor->req_bitmap, trans_id, 1);
> +	}

In the case where a specific match is required, and trans_id is
valid but the addr's do not match, it looks like this function will
return the addr that didn't match, without removing the entry.
Shouldn't it return VMBUS_RQST_ERROR in that case?

> +
> +	return req_addr;
> +}
> +EXPORT_SYMBOL_GPL(__vmbus_request_addr_match);
> +
> +/*
> + * vmbus_request_addr_match - Clears/removes @trans_id from the @channel's
> + * requestor, provided the memory address stored at @trans_id equals @rqst_addr
> + * (or provided @rqst_addr matches the sentinel value VMBUS_RQST_ADDR_ANY).
> + *
> + * Returns the memory address stored at @trans_id, or VMBUS_RQST_ERROR if
> + * @trans_id is not contained in the requestor.
> + *
> + * Acquires and releases the requestor spin lock.
> + */
> +u64 vmbus_request_addr_match(struct vmbus_channel *channel, u64 trans_id,
> +			     u64 rqst_addr)
> +{
> +	struct vmbus_requestor *rqstor = &channel->requestor;
> +	unsigned long flags;
> +	u64 req_addr;
> 
> +	spin_lock_irqsave(&rqstor->req_lock, flags);
> +	req_addr = __vmbus_request_addr_match(channel, trans_id, rqst_addr);
>  	spin_unlock_irqrestore(&rqstor->req_lock, flags);
> +
>  	return req_addr;
>  }
> +EXPORT_SYMBOL_GPL(vmbus_request_addr_match);
> +
> +/*
> + * vmbus_request_addr - Returns the memory address stored at @trans_id
> + * in @rqstor. Uses a spin lock to avoid race conditions.
> + * @channel: Pointer to the VMbus channel struct
> + * @trans_id: Request id sent back from Hyper-V. Becomes the requestor's
> + * next request id.
> + */
> +u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id)
> +{
> +	return vmbus_request_addr_match(channel, trans_id,
> VMBUS_RQST_ADDR_ANY);
> +}
>  EXPORT_SYMBOL_GPL(vmbus_request_addr);
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index a7cb596d893b1..c77d78f34b96a 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -788,6 +788,7 @@ struct vmbus_requestor {
> 
>  #define VMBUS_NO_RQSTOR U64_MAX
>  #define VMBUS_RQST_ERROR (U64_MAX - 1)
> +#define VMBUS_RQST_ADDR_ANY U64_MAX
>  /* NetVSC-specific */
>  #define VMBUS_RQST_ID_NO_RESPONSE (U64_MAX - 2)
>  /* StorVSC-specific */
> @@ -1042,6 +1043,10 @@ struct vmbus_channel {
>  };
> 
>  u64 vmbus_next_request_id(struct vmbus_channel *channel, u64 rqst_addr);
> +u64 __vmbus_request_addr_match(struct vmbus_channel *channel, u64 trans_id,
> +			       u64 rqst_addr);
> +u64 vmbus_request_addr_match(struct vmbus_channel *channel, u64 trans_id,
> +			     u64 rqst_addr);
>  u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id);
> 
>  static inline bool is_hvsock_channel(const struct vmbus_channel *c)
> --
> 2.25.1