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Network File System Version 4                                   C. Lever
Internet-Draft                                                    Oracle
Intended status: Informational                            August 8, 2016
Expires: February 9, 2017


    Using Remote Invalidation With RPC-Over-RDMA Transport Protocols
                    draft-cel-nfsv4-reminv-design-01

Abstract

   Remote Invalidation relieves requesters/initiators of some of the
   burden of preparing memory to be accessed remotely, thus reducing the
   latency of transactions that require the use of explicit RDMA
   operations.  This document considers how to introduce Remote
   Invalidation to RPC-over-RDMA transport protocols.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 9, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  General Requirements  . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Memory Management Extensions  . . . . . . . . . . . . . .   4
     2.2.  Registration Types  . . . . . . . . . . . . . . . . . . .   4
     2.3.  Selecting STags To Invalidate Remotely  . . . . . . . . .   5
     2.4.  Future Enhancements . . . . . . . . . . . . . . . . . . .   5
   3.  Remote Invalidation In Operation  . . . . . . . . . . . . . .   6
     3.1.  Determining Remote Invalidation Support Status  . . . . .   6
     3.2.  Selection Of Which STag To Invalidate Remotely  . . . . .   7
     3.3.  Backward-Direction Operation  . . . . . . . . . . . . . .   7
   4.  Protocol Elements . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Per Protocol Version Remote Invalidation  . . . . . . . .   8
     4.2.  Per Connection Remote Invalidation  . . . . . . . . . . .   9
     4.3.  Fixed Protocol Remote Invalidation  . . . . . . . . . . .   9
     4.4.  Per RPC Remote Invalidation (Single STag) . . . . . . . .  10
     4.5.  Per RPC Remote Invalidation (Multiple STags)  . . . . . .  11
     4.6.  Inter-RPC Remote Invalidation . . . . . . . . . . . . . .  12
   5.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .  12
     5.1.  General Considerations  . . . . . . . . . . . . . . . . .  13
     5.2.  Analysis And Discussion . . . . . . . . . . . . . . . . .  13
     5.3.  Example Remote Invalidation Protocol  . . . . . . . . . .  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Like other RDMA-enabled storage protocols, RPC-over-RDMA Version Two
   [I-D.cel-nfsv4-rpcrdma-version-two] employs a Read-Write transfer
   model when using explicit RDMA operations to transfer data.  This
   means an RPC-over-RDMA requester exposes regions of its memory to an
   RPC-over-RDMA responder, which then uses RDMA Read and Write
   operations to transfer bulk data payloads.

   In preparation for such a transfer, a requester asks its RNIC to
   assign a steering tag, or STag, to a region of memory containing the
   data to be moved.  At this time, access rights are granted that allow
   the RNIC to access or update that memory.  This act is referred to as
   memory "registration."  RNICs use STags to steer data to and from
   registered memory regions.




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   When data movement is complete, each STag is dissociated from its
   memory region.  This act is referred to as memory "invalidation."  It
   prevents further responder access to that memory region by revoking
   its remote access rights.  Invalidation must be done before RPC
   applications on the requester are allowed access to memory that was
   involved in an explicit RDMA operation.

   Remote Invalidation is a technique by which an RDMA peer can request
   that a remote RNIC invalidate an STag associated with memory on that
   remote peer [RFC5042].  An RDMA consumer requests Remote Invalidation
   by posting an RDMA Send With Invalidate Work Request in place of an
   RDMA Send Work Request.  RDMA Send With Invalidate is similar to RDMA
   Send, but takes one additional argument: a single STag to be
   invalidated by the RNIC that receives the sent message.  An RDMA Send
   message is transmitted with additional header information that
   conveys the STag that is to be invalidated [RFC5040].

   The benefit of Remote Invalidation is that an extra Work Request,
   context switch, and interrupt to perform memory invalidation are not
   required by the requester as part of handling the completion of an
   RPC transaction.  STag invalidation begins before the Receive
   completes, thus invalidation is started (and completes) sooner.  The
   upshot is faster completion of RPC transactions that involve
   registered memory.

   The primary issues at the RPC-over-RDMA protocol level are to provide
   a mechanism to indicate when Remote Invalidation can be used by the
   transport, and to provide selection criteria for choosing which STag
   to invalidate remotely.  To provide these, elements of the XDR
   definition of the RPC-over-RDMA protocol must be altered to some
   degree, depending on desired flexibility of operation, invasiveness
   of XDR changes, and broadness of hardware support.

   The purpose of this document is to explore generally how Remote
   Invalidation can be introduced into the RPC-over-RDMA transport
   protocol.  This document does not attempt to propose a detailed
   specification of any particular mechanism.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].








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2.  General Requirements

2.1.  Memory Management Extensions

   Remote Invalidation was not available in the original RDMA Verbs API.
   New verbs API objects were specified that include operations that
   enable Remote Invalidation, now described in [IB].  The Verbs API
   provides a capabilities flag, MEM_MGT_EXTENSIONS, that indicates that
   an RNIC can provide the new APIs and objects.

   Only an STag that was registered using the new FRWR mechanism, also
   only available with MEM_MGT_EXTENSIONS, may be invalidated remotely
   [RFC5040].

2.2.  Registration Types

   For the purposes of this discussion, there are two classes of STags.
   Dynamically-registered STags are used in a single RPC, then
   invalidated.  Persistently-registered STags live longer than one RPC.
   They are typically registered for the life of an RPC-over-RDMA
   connection, and sometimes even longer.

   In RPC-over-RDMA Version One, a requester may provide more than one
   STag in the chunk lists of an RPC.  It may provide any combination of
   the following registration types in one RPC, any combination of these
   in a series of RPCs on the same connection, or it may use some other
   registration model.

   Examples of persistently-registered STags include:

   1.  The device's local DMA rkey

   2.  An STag registered for that connection that doesn't change from
       RPC to RPC (for a utility buffer, say)

   3.  An STag registered for a fixed memory region that is updated each
       time it is advertised

   Examples of dynamically-registered STags include:

   1.  An STag registered for a single RPC using a non-FRWR mechanism,
       then invalidated when the RPC is retired

   2.  An STag registered for a single RPC using the FRWR mechanism,
       then immediately when the RPC is retired

   Among these examples, only the second type of dynamically-registered
   STags may be invalidated remotely.



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2.3.  Selecting STags To Invalidate Remotely

   Remote Invalidation implementations can be split into different
   styles:

   Fixed Protocol
      The choice of which STag to invalidate remotely is fixed in the
      protocol specification.

   Responder's Choice
      The responder chooses an STag to invalidate remotely from among
      all the STags in incoming requests.

   Requester's Choice
      The requester chooses one or more STags that may be invalidated
      remotely, indicating its choices in each request.  The responder
      chooses an STag to invalidate remotely from among the requester's
      picks.

   Outside of being told explicitly by the requester, there is no
   mechanism by which a responder can determine how a requester-provided
   STag was registered.  Thus a requester that mixes persistently- and
   dynamically-registered STags in one RPC, or mixes them across RPCs on
   the same connection, cannot tolerate Responder's Choice.

2.4.  Future Enhancements

   There are two related enhancements that further reduce the effort
   needed to invalidate STags associated with complex RPCs:

   o  The ability for one registered STag to represent a list of memory
      regions that are not contiguous

   o  The ability to specify more than one remote STag in a single Work
      Request to be remotely invalidated

   At this time, the first mechanism has been implemented in at least
   one RNIC on the market.  The second is speculative.

   Given support for registering non-contiguous memory regions with one
   STag, when an RPC-over-RDMA requester constructs an RPC that has both
   a Read list and a Write list, the requester has a choice:

   o  The requester can register a separate STag for each access mode
      (one STag for memory regions needing read access, and one STag for
      those needing write access) to provide good data security





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   o  The requester can register a single STag with read and write
      access enabled for the whole set of memory regions, to allow RDMA
      Send With Invalidate to work optimally

   Having the ability to remotely invalidate multiple STags at once
   enables the combination of optimal performance and optimal security.

3.  Remote Invalidation In Operation

   When requester memory is registered for remote access, an RPC-over-
   RDMA implementation could use Remote Invalidation by following these
   steps:

   1.  The requester DMA-maps a memory region that will participate in
       an RPC transaction, and registers an STag for that region.

   2.  The requester transmits the RPC Call, which also conveys the
       STag, to the responder.

   3.  The responder processes the RPC transaction.  The peer RNICs use
       the STag to move RPC arguments or results.

   4.  The responder transmits the RPC Reply using an RDMA Send With
       Invalidate Work Request, specifying the STag in the Work
       Request's inv_handle field.

   5.  A Receive Work Request completes on the requester, carrying this
       RPC reply, and reporting the invalidated STag.

   6.  The requester skips invalidation of the STag, then DMA-unmaps the
       memory region associated with the STag.

   The requester no longer needs to invalidate the STag involved with
   this RPC.  However, there are additional details that must be
   resolved before the use of Remote Invalidation can commence.

3.1.  Determining Remote Invalidation Support Status

   An RDMA consumer (an Upper Layer Protocol implementation) that does
   not support Remote Invalidation might not tolerate the use of RDMA
   Send With Invalidate by the transport layer.  Such a requester
   performs Local Invalidation on STags that already happen to be
   invalid, and in some cases this can result in protection errors or
   other issues.

   Thus, to avoid spurious connection termination, a responder must not
   post an RDMA Send With Invalidate Work Request unless it is sure the
   following three conditions are met:



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   o  The requester's RNIC is prepared to receive the additional header
      information associated with Remote Invalidation

   o  The requester has used FRWR to register STags it wants invalidated
      remotely

   o  The requester is prepared to recognize remotely invalidated STags
      and thus avoid invalidating them a second time

   When all three of these conditions are true, a requester can report
   positive Remote Invalidation support status to responders using an
   Upper Layer Protocol mechanism.  When a responder does not know the
   requester's Remote Invalidation support status, it cannot use Remote
   Invalidation without endangering the connection.

3.2.  Selection Of Which STag To Invalidate Remotely

   The RDMA Send With Invalidate Work Request invalidates only one STag.
   RPC-over-RDMA requesters may register more than one STag to handle
   the movement of payloads for a single RPC.  Either the client will
   have to specify which STag may be remotely invalidated, the protocol
   will have to specify a fixed way to select which STag to invalidate,
   or the responder will have to choose arbitrarily which STag to
   remotely invalidate.

   In some circumstances, requesters may wish to utilize STags during
   transactions that are registered using a mechanism that does not
   tolerate Remote Invalidation.  For example, an STag that is the
   requester's local DMA rkey should never be invalidated remotely.  If
   a responder attempts to invalidate a such an STag, the result is
   undefined, but the connection can be terminated or other failures can
   occur.

   Even with Remote Invalidation enabled, requesters remain responsible
   for ensuring all STags are invalid before RPC transactions complete.
   To avoid leaving STags registered, a requester must be prepared for
   the responder or the requester's own RNIC to have not invalidated any
   of an RPC's STags.  When there are multiple STags associated with a
   single RPC, a requester must be prepared for any number of STags to
   have been remotely invalidated, including zero.

3.3.  Backward-Direction Operation

   As of this writing, no current implementation supports direct data
   placement in the backward-direction.  However, existing protocol
   specifications do not forbid it [I-D.ietf-nfsv4-rfc5666bis]
   [I-D.ietf-nfsv4-rpcrdma-bidirection]
   [I-D.cel-nfsv4-rpcrdma-version-two].



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   When chunks are present in a backward-direction RPC request, Remote
   Invalidation allows the responder to trigger invalidation of a
   requester's STags as part of sending a reply, the same as in the
   forward direction.

   However, in the backward direction, the server acts as the requester,
   and the client is the responder.  The server's RNIC, therefore, must
   support receiving an IETH, and the server must have registered the
   STags with FRWR.  Thus the server must indicate its Remote
   Invalidation support status to the client (the opposite of forward
   direction Remote Invalidation).

4.  Protocol Elements

   In this section, a number of protocol variations are considered.
   These vary in functionality and invasiveness.  Some may be
   appropriate to use in combination.

4.1.  Per Protocol Version Remote Invalidation

4.1.1.  Description

   When a higher protocol version number is negotiated, Remote
   Invalidation is always enabled.  This new protocol version would then
   be usable only with RNICs that support Remote Invalidation.  Both
   peers assume that Remote Invalidation may be used in either
   direction.

4.1.2.  Similar Existing Implementations

   SMB Direct [MS-SMBD]

4.1.3.  Advantages

   No XDR changes or protocol extensions are required.

   Backward-direction use of Remote Invalidation is automatically
   supported.

4.1.4.  Disadvantages

   The requester is not in control of which STags in an RPC may be
   invalidated.  Thus, a requester must not advertise STags which must
   never be invalidated.

   Other features and benefits of the new protocol version would not be
   available when an implementation employs an RNIC that does not
   support Remote Invalidation.  In particular, RNICs that do not



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   support MEM_MGT_EXTENTIONS (i.e., FRWR) could not use the new
   protocol version.

   An extension or addition protocol version bump is required to
   indicate support for transport-level mechanisms that can invalidate
   multiple STags at once.

4.2.  Per Connection Remote Invalidation

4.2.1.  Description

   At connection initiation time, messages are exchanged that indicate
   each peer's Remote Invalidation support status.  Without these
   messages, peers assume Remote Invalidation is not supported.

4.2.2.  Similar Existing Implementations

   iSER [RFC7145].  Information is exchanged in RDMA-CM connection
   requests to report an implementation's Remote Invalidation support
   status.

4.2.3.  Advantages

   No changes to the base protocol XDR are required.

4.2.4.  Disadvantages

   Out-of-band messages are required to establish support status.

   The requester is not in control of which STags in an RPC may be
   invalidated.  Thus, a requester must not advertise STags which must
   never be invalidated.

   To support backward-direction operation, the server must separately
   indicate that it supports Remote Invalidation.

   To enable support for multiple STag invalidation, this negotiation
   protocol would have to be extended again to indicate when mechanisms
   other than RDMA Send With Invalidate are supported by the requester's
   RNIC.

4.3.  Fixed Protocol Remote Invalidation

4.3.1.  Description

   No new field is introduced to the transport header.  Protocol
   specification determines how the responder chooses which STag is to




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   be invalidated remotely.  Some other means is used to determine
   whether Remote Invalidation can be used or not.

4.3.2.  Similar Existing Implementations

   iSER [RFC7145].  Two STags fields appear in each request: one
   advertises Read data and one advertises Write data.  When only one
   STag is used in the request, it may be invalidated remotely.  One
   both STags are used, only the Read STag may be invalidated remotely.

4.3.3.  Advantages

   No changes to the base protocol XDR are required.

4.3.4.  Disadvantages

   Out-of-band messages are required to establish support status.

   The requester is not in control of which STags in an RPC may be
   invalidated.  Thus, a requester must not advertise STags which must
   never be invalidated.

   This mechanism may not work well for transport protocols that allow
   multiple read and write STags.

4.4.  Per RPC Remote Invalidation (Single STag)

4.4.1.  Description

   A field is added to the transport header that contains an STag which
   may be invalidated by the responder.  A special value can be chosen
   to mean "no STag may be invalidated" for use by requesters that have
   no support for Remote Invalidation.

4.4.2.  Similar Existing Implementations

   None.

4.4.3.  Advantages

   A requester may advertise STags that cannot be invalidated remotely,
   as long as they are never marked as "may invalidate."

   No out-of-band support status negotiation is needed.

   Backward-direction RPCs can each indicate whether a backward-
   direction requester desires or does not support Remote Invalidation.




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   The responder needs no special logic or assumptions to choose the
   STag to invalidate remotely.

4.4.4.  Disadvantages

   Either the base RPC-over-RDMA header XDR definition is altered, or a
   protocol extension is required.

   Requesters transmit a little extra data per RPC, making RPC-over-RDMA
   messages slightly more costly to send and parse.

   This mechanism cannot support the remote invalidation of multiple
   STags at once.

4.5.  Per RPC Remote Invalidation (Multiple STags)

4.5.1.  Description

   A new data structure is added to the transport header that indicate
   which STags which may be invalidated by the responder.

   This information might appear as a new field in the RDMA segment data
   structure, as each segment has its own STag field.  The field
   indicates whether or not that STag may be invalidated by the
   responder.  Perhaps that field is a boolean, though in XDR, a boolean
   is a full 32 bits.

   Or, this information could appear in the header as an array of STags,
   to reduce the amount of extra data contained in the RPC-over-RDMA
   header.  Zero array elements means the requester does not support
   Remote Invalidation.

4.5.2.  Similar Existing Implementations

   NVMe/Fabrics [NVME].  Each STag in a request has an associated bit
   flag that indicates whether the responder is allowed to invalidate it
   remotely.

4.5.3.  Advantages

   A requester may advertise STags that cannot be invalidated remotely,
   as long as they are never marked as "may invalidate."

   The mechanism allows a requester to request either invalidation of
   multiple STags at once, or to choose one STag to invalidate remotely.

   No out-of-band support status negotiation is needed.




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   Each backward-direction RPC can indicate whether a backward-direction
   requester desires or does not support Remote Invalidation.

   The responder needs no special logic or assumptions to choose the
   STag to invalidate remotely.

4.5.4.  Disadvantages

   The RPC-over-RDMA header XDR definition is possibly extensively
   altered.

   Requesters transmit extra data per RPC.  However, it is limited to
   only one or two 32-bit words in most cases.

4.6.  Inter-RPC Remote Invalidation

4.6.1.  Description

   As a subfeature of support for Remote Invalidation, it is possible
   that a responder can remotely invalidate an STag (using RDMA Send
   With Invalidate) that refers to registered memory being used in the
   Read chunk of a different RPC.  Such Remote Invalidation would be
   requested only after the RDMA Read has already been completed.

   This can be useful when a responder is replying to an RPC via an
   inline message, but notices there are other RPC replies pending that
   have multiple STags, some of which are Read chunks.

4.6.2.  Similar Existing Implementations

   None

4.6.3.  Advantages

   This is one way to enable remote invalidation of multiple STags per
   RPC, using only RDMA Send With Invalidate.

4.6.4.  Disadvantages

   Additional requester and responder complexity would be required to
   keep track of STags.

5.  Recommendations








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5.1.  General Considerations

   When constructing a protocol to support Remote Invalidation, one of
   these designs, or some combination of them, can be chosen.

   In no particular order, the design priorities are:

   o  Do not prevent the efficient operation of RNICs that do not handle
      RDMA Send With Invalidate

   o  Introduce as little impact on header XDR and header length as
      possible, to keep collateral performance impact low

   o  Enable support for Remote Invalidation when explicit RDMA is used
      in backward-direction RPCs.

   An important question is whether the base RPC-over-RDMA Version Two
   protocol should support Remote Invalidation, whether Remote
   Invalidation support should be carried entirely on the shoulders of
   protocol extensions, or whether some combination of the two is best.

   Upper Layer Protocols will likely always be responsible for some
   degree of signaling Remote Invalidation capabilities, as long as
   innovation continues at the transport layer (e.g., new RDMA
   operations that enable Remote Invalidation).  Future hardware
   capabilities are perpetually hazy, limiting the ability to design
   long-lived protocol support for them.  Lastly, it is difficult to
   estimate how long the industry must continue to support less capable
   devices.

5.2.  Analysis And Discussion

   All things being equal, making no changes to the base XDR definition
   has great appeal.  If the mechanism in Section 4.2 can be broadly
   effective at enabling Remote Invalidation in the current set of RPC-
   over-RDMA implementations, it would be the proper choice.

   Unfortunately, among current RPC-over-RDMA client implementations,
   there is one client that can immediately use a per-connection style
   protocol, and one that can use only a per-RPC style protocol such as
   Section 4.4.  A third known client resides in user space and is thus
   incapable of using the FRWR registration mechanism.

   Because there is a wide latitude of implementation choice already
   allowed by the RPC-over-RDMA transport protocol, the author's
   preference is to implement Section 4.4.  The target STag can be added
   to the rpcrdma2_chunk_lists data structure as a single field.  No
   further changes or extensions are needed.



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   In the longer term, the requester appears to be in the better
   position to determine which STag may be invalidated remotely.  With
   this mechanism, the requester can choose based on which STags may be
   invalidated remotely, or may use criteria based on the strengths of
   its RNIC.  For instance, choosing the largest registered memory
   region might be beneficial in some cases.

   Allowing the responder to select from among several choices does not
   seem to bring additional value, and burdens the responder with
   additional header parsing costs for each chunk-bearing RPC reply.

   Furthermore, the ability to request Remote Invalidation of multiple
   STags in a single Work Request appears to be somewhat distant.  It
   would require additional Upper Layer Protocol mechanisms to
   distinguish the new mechanism from using RDMA Send With Invalidate,
   which we are not in a position to design today.  Thus it does not
   seem worth the extra implementation and protocol complexity of having
   the requester provide a list of STags for the responder to choose
   from.

   Allowing the feature described in Section 4.6 is likely to increase
   the complexity of responder and especially requester implementations,
   as they would have to remember invalidated STags independently of RPC
   completions.  Because it does not require any XDR changes, it could
   easily be enabled in a future protocol extension.  The author's
   preference is to forbid this behavior in the initial specification,
   but allow for a future extension to introduce it.

5.3.  Example Remote Invalidation Protocol

   As an example of how to proceed, the simplest approach would replace
   struct rpcrdma2_chunk_lists (as defined in
   [I-D.cel-nfsv4-rpcrdma-version-two]) with the following:


   <CODE BEGINS>

    struct rpcrdma2_chunk_lists {
        enum msg_type               rdma_direction;
        u32                         rdma_inv_handle;
        struct rpcrdma2_read_list   *rdma_reads;
        struct rpcrdma2_write_list  *rdma_writes;
        struct rpcrdma2_write_chunk *rdma_reply;
    };

   <CODE ENDS>





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   The following language describes how to utilize the new field:

      The requester sets the value of the rdma_inv_handle field to the
      value of any one of the rdma_handle fields in the RPC-over-RDMA
      header of the RPC call that may be invalidated remotely.  If the
      RPC-over-RDMA header of the RPC call contains no rdma_handles that
      may be invalidated remotely, the requester MUST set the value of
      the rdma_inv_handle field to zero.  The requester MUST NOT set the
      value of the rdma_inv_handle field to the value of an rdma_handle
      that cannot be invalidated remotely.

      As part of forming the RPC-over-RDMA header for the reply, the
      responder copies the value of the rdma_inv_handle field from the
      RPC-over-RDMA header of the matching RPC call.  If the
      rdma_inv_handle field in the RPC-over-RDMA header of an RPC call
      contains zero, the responder MUST NOT use RDMA Send With
      Invalidate to transmit the matching RPC reply.  Otherwise, the
      responder SHOULD use RDMA Send With Invalidate to transmit the
      reply to this RPC, specifying the value in the RPC-over-RDMA
      header's rdma_inv_handle field as the Work Request's inv_rkey.
      The responder MUST NOT specify any other value in the Work
      Request's inv_rkey field.

6.  IANA Considerations

   There are no IANA considerations for this document.

7.  Security Considerations

   Remote Invalidation metadata is conveyed in the clear in RPC-over-
   RDMA headers.  This does not expose any new information to attackers.

   A man-in-the-middle can alter Remote Invalidation metadata while it
   is in transit.  Requesters are prepared to handle the case where
   responders have not invalidated any STags associated with an RPC.  An
   attacker can cause other STags in flight to be invalidated before the
   responder is finished with the associated memory.  Or an attacker can
   replace the "to-be invalidated" STag with an STag in the same RPC
   that should not be invalidated remotely.  Any of these might cause
   loss of connection, or other failures.

   A connection relationship is required to exist between a requester
   and a responder.  The requester's RNIC has associated a Protection
   Domain with that connection.  The STag on the requester to be
   invalidated is associated with that Protection Domain.  This protects
   against arbitrary invalidation of STags by network nodes not part of
   the connection.




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   Further discussion appears in [RFC5042].

8.  Acknowledgments

   The author wishes to thank Sagi Grimberg, Christoph Hellwig, Dave
   Noveck, and Tom Talpey.  Special thanks go to nfsv4 Working Group
   Chair Spencer Shepler and nfsv4 Working Group Secretary Thomas Haynes
   for their support.

9.  References

9.1.  Normative References

   [I-D.cel-nfsv4-rpcrdma-version-two]
              Lever, C. and D. Noveck, "RPC-over-RDMA Version Two
              Protocol", draft-cel-nfsv4-rpcrdma-version-two-01 (work in
              progress), June 2016.

   [I-D.ietf-nfsv4-rfc5666bis]
              Lever, C., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call, Version
              One", draft-ietf-nfsv4-rfc5666bis-07 (work in progress),
              May 2016.

   [I-D.ietf-nfsv4-rpcrdma-bidirection]
              Lever, C., "Bi-directional Remote Procedure Call On RPC-
              over-RDMA Transports", draft-ietf-nfsv4-rpcrdma-
              bidirection-05 (work in progress), June 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5040]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, DOI 10.17487/RFC5040, October
              2007, <http://www.rfc-editor.org/info/rfc5040>.

   [RFC5042]  Pinkerton, J. and E. Deleganes, "Direct Data Placement
              Protocol (DDP) / Remote Direct Memory Access Protocol
              (RDMAP) Security", RFC 5042, DOI 10.17487/RFC5042, October
              2007, <http://www.rfc-editor.org/info/rfc5042>.








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   [RFC7145]  Ko, M. and A. Nezhinsky, "Internet Small Computer System
              Interface (iSCSI) Extensions for the Remote Direct Memory
              Access (RDMA) Specification", RFC 7145,
              DOI 10.17487/RFC7145, April 2014,
              <http://www.rfc-editor.org/info/rfc7145>.

9.2.  Informative References

   [IB]       InfiniBand Trade Association, "InfiniBand Architecture
              Specifications", <http://www.infinibandta.org>.

   [MS-SMBD]  Microsoft Corporation, "SMB Remote Direct Memory Access
              (RDMA) Transport Protocol Specification", July 2016.

   [NVME]     NVM Express, Inc., "NVM Express Revision 1.2.1", July
              2016.

Author's Address

   Charles Lever
   Oracle Corporation
   1015 Granger Avenue
   Ann Arbor, MI  48104
   USA

   Phone: +1 734 274 2396
   Email: chuck.lever@oracle.com
























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