Re: [PATCH for-next v3 3/4] RDMA/efa: User/kernel compatibility handshake mechanism

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Jul 22, 2020 at 03:04:20PM +0300, Gal Pressman wrote:
> On 22/07/2020 14:55, Jason Gunthorpe wrote:
> > On Tue, Jul 21, 2020 at 04:30:48PM +0300, Gal Pressman wrote:
> >> Introduce a mechanism that performs an handshake between the userspace
> >> provider and kernel driver which verifies that the user supports all
> >> required features in order to operate correctly.
> >>
> >> The handshake verifies the needed functionality by comparing the
> >> reported device caps and the provider caps. If the device reports a
> >> non-zero capability the appropriate comp mask is required from the
> >> userspace provider in order to allocate the context.
> >>
> >> Reviewed-by: Shadi Ammouri <sammouri@amazon.com>
> >> Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
> >> Signed-off-by: Gal Pressman <galpress@amazon.com>
> >>  drivers/infiniband/hw/efa/efa_verbs.c | 49 +++++++++++++++++++++++++++
> >>  include/uapi/rdma/efa-abi.h           | 10 ++++++
> >>  2 files changed, 59 insertions(+)
> >>
> >> diff --git a/drivers/infiniband/hw/efa/efa_verbs.c b/drivers/infiniband/hw/efa/efa_verbs.c
> >> index 26102ab333b2..7ca40df81ee5 100644
> >> +++ b/drivers/infiniband/hw/efa/efa_verbs.c
> >> @@ -1501,11 +1501,48 @@ static int efa_dealloc_uar(struct efa_dev *dev, u16 uarn)
> >>  	return efa_com_dealloc_uar(&dev->edev, &params);
> >>  }
> >>  
> >> +#define EFA_CHECK_COMP(_dev, _comp_mask, _attr, _mask)                         \
> >> +	(!(_dev)->dev_attr._attr || ((_comp_mask) & (_mask)))
> >> +
> >> +#define DEFINE_COMP_HANDSHAKE(_dev, _comp_mask, _attr, _mask)                  \
> >> +	{                                                                      \
> >> +		.attr = #_attr,                                                \
> >> +		.check_comp = EFA_CHECK_COMP(_dev, _comp_mask, _attr, _mask)   \
> >> +	}
> >> +
> >> +int efa_user_comp_handshake(const struct ib_ucontext *ibucontext,
> >> +			    const struct efa_ibv_alloc_ucontext_cmd *cmd)
> >> +{
> >> +	struct efa_dev *dev = to_edev(ibucontext->device);
> >> +	int i;
> >> +	struct {
> >> +		char *attr;
> >> +		bool check_comp;
> >> +	} user_comp_handshakes[] = {
> >> +		DEFINE_COMP_HANDSHAKE(dev, cmd->comp_mask, max_tx_batch,
> >> +				      EFA_ALLOC_UCONTEXT_CMD_COMP_TX_BATCH),
> >> +		DEFINE_COMP_HANDSHAKE(dev, cmd->comp_mask, min_sq_depth,
> >> +				      EFA_ALLOC_UCONTEXT_CMD_COMP_MIN_SQ_WR),
> >> +	};
> > 
> > This seems like a very expensive construct
> > 
> > Why have the array at all? Just list the macros and have them jump to
> > err
> 
> Do you mean:
> 
> if (CHECK_COMP(x1)) {
>     ibdev_dbg(err);
>     goto err;
> }
> 
> if (CHECK_COMP(x2)) {
>     ibdev_dbg(err);
>     goto err;
> }
> 
> [...]
> 
> That adds much more boilerplate code for each feature. Or do you have something
> else in mind?

#define DO_COMP_HANDSHAKE() \
    if (...) goto err

DO_COMP_HANDSHAKE(x1)
DO_COMP_HANDSHAKE(2)

Jason