Re: [PATCHv8 07/11] ib_core: Add API to support IBoE from userspace

[Eli Cohen <eli-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On Wed, May 12, 2010 at 01:28:31PM -0700, Roland Dreier wrote:
>  > Add ib_uverbs_get_eth_l2_addr() to allow ibv_create_ah() to resolve <sgid,
>  > dgid> to <vlan, dmac> for any gid type.  Although user-space might bypass this
>  > call for link-local gids, it is better not to replicate the kernel resolution
>  > policy.  Port link layer is also returned by ibv_query_port().
> 
> A high-level comment/question, followed by some notes about the specific patch.
> 
> At the highest level, is having this very low-level command exposed as
> part of the kernel uverbs <-> userspace API the right place to split
> things?  Making the Ethernet address resolution part of the low-level
> driver implies that it's not really a generic part of the verbs interface.

Correct - Ethernet address resolution really isn't part of the verbs
interface accoring to the RoCE specification; it should happen below
the verbs.

> 
> Maybe it is generic, and we should have a generic function instead of
> calling into the low-level driver.  I see the argument that we should
> keep the policy in the kernel, although I'm not sure how strong that
> argument is -- once we start shipping a kernel with a certain policy
> (and I guess OFED has in effect already done that), how could we ever
> change that policy?  We'll have interoperability issues anyway, so it
> seems having userspace and kernel use different policies doesn't cause
> much further problems anyway.

Address mapping policies depend on the address type. This patch only
defines a policy for mapping link-local addresses, and we should
indeed take care not to change it (if possible).
Later on, we can add more policies for other address types (e.g.,
normal IPv6 addresses, mapped IPv4 addresses, etc.)
> 
> Or maybe it is device-specific, and we could wrap it up into the create
> AH uverbs call we already have?

Interesting idea. Not sure what is better here: a seperate ABI
call or some additional 'u8 ctx[32]' field in struct
ib_uverbs_create_ah_resp that will be interpreted by the hw-specific
user-space driver.

> 
> Low-level comments:
> 
>  > +ssize_t ib_uverbs_get_eth_l2_addr(struct ib_uverbs_file *file, const char __user *buf,
>  > +				  int in_len, int out_len)
>  > +{
>  > +	struct ib_uverbs_get_eth_l2_addr       cmd;
>  > +	struct ib_uverbs_get_eth_l2_addr_resp  resp;
>  > +	int              ret;
>  > +	struct ib_pd    *pd;
>  > +
>  > +	if (out_len < sizeof resp)
>  > +		return -ENOSPC;
>  > +
>  > +	if (copy_from_user(&cmd, buf, sizeof cmd))
>  > +		return -EFAULT;
>  > +
>  > +	pd = idr_read_pd(cmd.pd_handle, file->ucontext);
>  > +	if (!pd)
>  > +		return -EINVAL;
>  > +
>  > +	ret = ib_get_eth_l2_addr(pd->device, cmd.port, (union ib_gid *)cmd.gid,
>  > +				 cmd.sgid_idx, resp.mac, &resp.vlan_id, &resp.tagged);
>  > +	put_pd_read(pd);
>  > +	if (!ret) {
>  > +		if (copy_to_user((void __user *) (unsigned long) cmd.response,
>  > +				 &resp, sizeof resp))
>  > +			return -EFAULT;
> 
> This leaks kernel memory contents to userspace since the stack variable
> resp is never cleared.  Also will cause problems if we ever need to use
> the reserved fields for anything.

I see, I missed that subtle detail.


> 
> Also I'm not sure I understand why you pass the PD into this method?  It
> seems you just use it to get a pointer to the device, but you already
> have that from the uverbs_file structure that's passed into all commands.

True, missed that too.

> 
>  > +int ib_get_eth_l2_addr(struct ib_device *device, u8 port, union ib_gid *gid,
>  > +		       int sgid_idx, u8 *mac, __u16 *vlan_id, u8 *tagged)
>  > +{
>  > +	if (!device->get_eth_l2_addr)
>  > +		return -ENOSYS;
>  > +
>  > +	return device->get_eth_l2_addr(device, port, gid, sgid_idx, mac, vlan_id, tagged);
>  > +}
>  > +EXPORT_SYMBOL(ib_get_eth_l2_addr);
> 
> I don't think we need this wrapper, since uverbs can just call the
> get_eth_l2_addr method directly (we already do that for quite a few
> other methods, eg alloc_ucontext is a uverbs-only method that has no
> in-kernel wrapper).  Also the -ENOSYS test isn't necessary, since a
> device-driver shouldn't allow this method unless it actually implements
> it.
> 
I agree.

By the way, do you prefer that I re-create the patch with the fixes or
would you make the necessary changes.

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