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

Michael Kelley (LINUX)
2022-04-08T15:25:59Z

From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> 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@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
> 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