FreeBSD/Linux Kernel Cross Reference
sys/contrib/xen/grant_table.h

     /******************************************************************************
      * grant_table.h
      *
      * Interface for granting foreign access to page frames, and receiving
      * page-ownership transfers.
      *
      * Permission is hereby granted, free of charge, to any person obtaining a copy
      * of this software and associated documentation files (the "Software"), to
      * deal in the Software without restriction, including without limitation the
     * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
     * sell copies of the Software, and to permit persons to whom the Software is
     * furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included in
     * all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     * DEALINGS IN THE SOFTWARE.
     *
     * Copyright (c) 2004, K A Fraser
     */
    
    #ifndef __XEN_PUBLIC_GRANT_TABLE_H__
    #define __XEN_PUBLIC_GRANT_TABLE_H__
    
    #include "xen.h"
    
    /*
     * `incontents 150 gnttab Grant Tables
     *
     * Xen's grant tables provide a generic mechanism to memory sharing
     * between domains. This shared memory interface underpins the split
     * device drivers for block and network IO.
     *
     * Each domain has its own grant table. This is a data structure that
     * is shared with Xen; it allows the domain to tell Xen what kind of
     * permissions other domains have on its pages. Entries in the grant
     * table are identified by grant references. A grant reference is an
     * integer, which indexes into the grant table. It acts as a
     * capability which the grantee can use to perform operations on the
     * granter's memory.
     *
     * This capability-based system allows shared-memory communications
     * between unprivileged domains. A grant reference also encapsulates
     * the details of a shared page, removing the need for a domain to
     * know the real machine address of a page it is sharing. This makes
     * it possible to share memory correctly with domains running in
     * fully virtualised memory.
     */
    
    /***********************************
     * GRANT TABLE REPRESENTATION
     */
    
    /* Some rough guidelines on accessing and updating grant-table entries
     * in a concurrency-safe manner. For more information, Linux contains a
     * reference implementation for guest OSes (drivers/xen/grant_table.c, see
     * http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=drivers/xen/grant-table.c;hb=HEAD
     *
     * NB. WMB is a no-op on current-generation x86 processors. However, a
     *     compiler barrier will still be required.
     *
     * Introducing a valid entry into the grant table:
     *  1. Write ent->domid.
     *  2. Write ent->frame:
     *      GTF_permit_access:   Frame to which access is permitted.
     *      GTF_accept_transfer: Pseudo-phys frame slot being filled by new
     *                           frame, or zero if none.
     *  3. Write memory barrier (WMB).
     *  4. Write ent->flags, inc. valid type.
     *
     * Invalidating an unused GTF_permit_access entry:
     *  1. flags = ent->flags.
     *  2. Observe that !(flags & (GTF_reading|GTF_writing)).
     *  3. Check result of SMP-safe CMPXCHG(&ent->flags, flags, 0).
     *  NB. No need for WMB as reuse of entry is control-dependent on success of
     *      step 3, and all architectures guarantee ordering of ctrl-dep writes.
     *
     * Invalidating an in-use GTF_permit_access entry:
     *  This cannot be done directly. Request assistance from the domain controller
     *  which can set a timeout on the use of a grant entry and take necessary
     *  action. (NB. This is not yet implemented!).
     *
     * Invalidating an unused GTF_accept_transfer entry:
     *  1. flags = ent->flags.
     *  2. Observe that !(flags & GTF_transfer_committed). [*]
     *  3. Check result of SMP-safe CMPXCHG(&ent->flags, flags, 0).
     *  NB. No need for WMB as reuse of entry is control-dependent on success of
     *      step 3, and all architectures guarantee ordering of ctrl-dep writes.
     *  [*] If GTF_transfer_committed is set then the grant entry is 'committed'.
     *      The guest must /not/ modify the grant entry until the address of the
     *      transferred frame is written. It is safe for the guest to spin waiting
     *      for this to occur (detect by observing GTF_transfer_completed in
     *      ent->flags).
    *
    * Invalidating a committed GTF_accept_transfer entry:
    *  1. Wait for (ent->flags & GTF_transfer_completed).
    *
    * Changing a GTF_permit_access from writable to read-only:
    *  Use SMP-safe CMPXCHG to set GTF_readonly, while checking !GTF_writing.
    *
    * Changing a GTF_permit_access from read-only to writable:
    *  Use SMP-safe bit-setting instruction.
    */
   
   /*
    * Reference to a grant entry in a specified domain's grant table.
    */
   typedef uint32_t grant_ref_t;
   
   /*
    * A grant table comprises a packed array of grant entries in one or more
    * page frames shared between Xen and a guest.
    * [XEN]: This field is written by Xen and read by the sharing guest.
    * [GST]: This field is written by the guest and read by Xen.
    */
   
   /*
    * Version 1 of the grant table entry structure is maintained largely for
    * backwards compatibility.  New guests are recommended to support using
    * version 2 to overcome version 1 limitations, but to default to version 1.
    */
   #if __XEN_INTERFACE_VERSION__ < 0x0003020a
   #define grant_entry_v1 grant_entry
   #define grant_entry_v1_t grant_entry_t
   #endif
   struct grant_entry_v1 {
       /* GTF_xxx: various type and flag information.  [XEN,GST] */
       uint16_t flags;
       /* The domain being granted foreign privileges. [GST] */
       domid_t  domid;
       /*
        * GTF_permit_access: GFN that @domid is allowed to map and access. [GST]
        * GTF_accept_transfer: GFN that @domid is allowed to transfer into. [GST]
        * GTF_transfer_completed: MFN whose ownership transferred by @domid
        *                         (non-translated guests only). [XEN]
        */
       uint32_t frame;
   };
   typedef struct grant_entry_v1 grant_entry_v1_t;
   
   /* The first few grant table entries will be preserved across grant table
    * version changes and may be pre-populated at domain creation by tools.
    */
   #define GNTTAB_NR_RESERVED_ENTRIES     8
   #define GNTTAB_RESERVED_CONSOLE        0
   #define GNTTAB_RESERVED_XENSTORE       1
   
   /*
    * Type of grant entry.
    *  GTF_invalid: This grant entry grants no privileges.
    *  GTF_permit_access: Allow @domid to map/access @frame.
    *  GTF_accept_transfer: Allow @domid to transfer ownership of one page frame
    *                       to this guest. Xen writes the page number to @frame.
    *  GTF_transitive: Allow @domid to transitively access a subrange of
    *                  @trans_grant in @trans_domid.  No mappings are allowed.
    */
   #define GTF_invalid         (0U<<0)
   #define GTF_permit_access   (1U<<0)
   #define GTF_accept_transfer (2U<<0)
   #define GTF_transitive      (3U<<0)
   #define GTF_type_mask       (3U<<0)
   
   /*
    * Subflags for GTF_permit_access and GTF_transitive.
    *  GTF_readonly: Restrict @domid to read-only mappings and accesses. [GST]
    *  GTF_reading: Grant entry is currently mapped for reading by @domid. [XEN]
    *  GTF_writing: Grant entry is currently mapped for writing by @domid. [XEN]
    * Further subflags for GTF_permit_access only.
    *  GTF_PAT, GTF_PWT, GTF_PCD: (x86) cache attribute flags to be used for
    *                             mappings of the grant [GST]
    *  GTF_sub_page: Grant access to only a subrange of the page.  @domid
    *                will only be allowed to copy from the grant, and not
    *                map it. [GST]
    */
   #define _GTF_readonly       (2)
   #define GTF_readonly        (1U<<_GTF_readonly)
   #define _GTF_reading        (3)
   #define GTF_reading         (1U<<_GTF_reading)
   #define _GTF_writing        (4)
   #define GTF_writing         (1U<<_GTF_writing)
   #define _GTF_PWT            (5)
   #define GTF_PWT             (1U<<_GTF_PWT)
   #define _GTF_PCD            (6)
   #define GTF_PCD             (1U<<_GTF_PCD)
   #define _GTF_PAT            (7)
   #define GTF_PAT             (1U<<_GTF_PAT)
   #define _GTF_sub_page       (8)
   #define GTF_sub_page        (1U<<_GTF_sub_page)
   
   /*
    * Subflags for GTF_accept_transfer:
    *  GTF_transfer_committed: Xen sets this flag to indicate that it is committed
    *      to transferring ownership of a page frame. When a guest sees this flag
    *      it must /not/ modify the grant entry until GTF_transfer_completed is
    *      set by Xen.
    *  GTF_transfer_completed: It is safe for the guest to spin-wait on this flag
    *      after reading GTF_transfer_committed. Xen will always write the frame
    *      address, followed by ORing this flag, in a timely manner.
    */
   #define _GTF_transfer_committed (2)
   #define GTF_transfer_committed  (1U<<_GTF_transfer_committed)
   #define _GTF_transfer_completed (3)
   #define GTF_transfer_completed  (1U<<_GTF_transfer_completed)
   
   /*
    * Version 2 grant table entries.  These fulfil the same role as
    * version 1 entries, but can represent more complicated operations.
    * Any given domain will have either a version 1 or a version 2 table,
    * and every entry in the table will be the same version.
    *
    * The interface by which domains use grant references does not depend
    * on the grant table version in use by the other domain.
    */
   #if __XEN_INTERFACE_VERSION__ >= 0x0003020a
   /*
    * Version 1 and version 2 grant entries share a common prefix.  The
    * fields of the prefix are documented as part of struct
    * grant_entry_v1.
    */
   struct grant_entry_header {
       uint16_t flags;
       domid_t  domid;
   };
   typedef struct grant_entry_header grant_entry_header_t;
   
   /*
    * Version 2 of the grant entry structure.
    */
   union grant_entry_v2 {
       grant_entry_header_t hdr;
   
       /*
        * This member is used for V1-style full page grants, where either:
        *
        * -- hdr.type is GTF_accept_transfer, or
        * -- hdr.type is GTF_permit_access and GTF_sub_page is not set.
        *
        * In that case, the frame field has the same semantics as the
        * field of the same name in the V1 entry structure.
        */
       struct {
           grant_entry_header_t hdr;
           uint32_t pad0;
           uint64_t frame;
       } full_page;
   
       /*
        * If the grant type is GTF_grant_access and GTF_sub_page is set,
        * @domid is allowed to access bytes [@page_off,@page_off+@length)
        * in frame @frame.
        */
       struct {
           grant_entry_header_t hdr;
           uint16_t page_off;
           uint16_t length;
           uint64_t frame;
       } sub_page;
   
       /*
        * If the grant is GTF_transitive, @domid is allowed to use the
        * grant @gref in domain @trans_domid, as if it was the local
        * domain.  Obviously, the transitive access must be compatible
        * with the original grant.
        *
        * The current version of Xen does not allow transitive grants
        * to be mapped.
        */
       struct {
           grant_entry_header_t hdr;
           domid_t trans_domid;
           uint16_t pad0;
           grant_ref_t gref;
       } transitive;
   
       uint32_t __spacer[4]; /* Pad to a power of two */
   };
   typedef union grant_entry_v2 grant_entry_v2_t;
   
   typedef uint16_t grant_status_t;
   
   #endif /* __XEN_INTERFACE_VERSION__ */
   
   /***********************************
    * GRANT TABLE QUERIES AND USES
    */
   
   /* ` enum neg_errnoval
    * ` HYPERVISOR_grant_table_op(enum grant_table_op cmd,
    * `                           void *args,
    * `                           unsigned int count)
    * `
    *
    * @args points to an array of a per-command data structure. The array
    * has @count members
    */
   
   /* ` enum grant_table_op { // GNTTABOP_* => struct gnttab_* */
   #define GNTTABOP_map_grant_ref        0
   #define GNTTABOP_unmap_grant_ref      1
   #define GNTTABOP_setup_table          2
   #define GNTTABOP_dump_table           3
   #define GNTTABOP_transfer             4
   #define GNTTABOP_copy                 5
   #define GNTTABOP_query_size           6
   #define GNTTABOP_unmap_and_replace    7
   #if __XEN_INTERFACE_VERSION__ >= 0x0003020a
   #define GNTTABOP_set_version          8
   #define GNTTABOP_get_status_frames    9
   #define GNTTABOP_get_version          10
   #define GNTTABOP_swap_grant_ref       11
   #define GNTTABOP_cache_flush          12
   #endif /* __XEN_INTERFACE_VERSION__ */
   /* ` } */
   
   /*
    * Handle to track a mapping created via a grant reference.
    */
   typedef uint32_t grant_handle_t;
   
   /*
    * GNTTABOP_map_grant_ref: Map the grant entry (<dom>,<ref>) for access
    * by devices and/or host CPUs. If successful, <handle> is a tracking number
    * that must be presented later to destroy the mapping(s). On error, <status>
    * is a negative status code.
    * NOTES:
    *  1. If GNTMAP_device_map is specified then <dev_bus_addr> is the address
    *     via which I/O devices may access the granted frame.
    *  2. If GNTMAP_host_map is specified then a mapping will be added at
    *     either a host virtual address in the current address space, or at
    *     a PTE at the specified machine address.  The type of mapping to
    *     perform is selected through the GNTMAP_contains_pte flag, and the
    *     address is specified in <host_addr>.
    *  3. Mappings should only be destroyed via GNTTABOP_unmap_grant_ref. If a
    *     host mapping is destroyed by other means then it is *NOT* guaranteed
    *     to be accounted to the correct grant reference!
    */
   struct gnttab_map_grant_ref {
       /* IN parameters. */
       uint64_t host_addr;
       uint32_t flags;               /* GNTMAP_* */
       grant_ref_t ref;
       domid_t  dom;
       /* OUT parameters. */
       int16_t  status;              /* => enum grant_status */
       grant_handle_t handle;
       uint64_t dev_bus_addr;
   };
   typedef struct gnttab_map_grant_ref gnttab_map_grant_ref_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_map_grant_ref_t);
   
   /*
    * GNTTABOP_unmap_grant_ref: Destroy one or more grant-reference mappings
    * tracked by <handle>. If <host_addr> or <dev_bus_addr> is zero, that
    * field is ignored. If non-zero, they must refer to a device/host mapping
    * that is tracked by <handle>
    * NOTES:
    *  1. The call may fail in an undefined manner if either mapping is not
    *     tracked by <handle>.
    *  3. After executing a batch of unmaps, it is guaranteed that no stale
    *     mappings will remain in the device or host TLBs.
    */
   struct gnttab_unmap_grant_ref {
       /* IN parameters. */
       uint64_t host_addr;
       uint64_t dev_bus_addr;
       grant_handle_t handle;
       /* OUT parameters. */
       int16_t  status;              /* => enum grant_status */
   };
   typedef struct gnttab_unmap_grant_ref gnttab_unmap_grant_ref_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_unmap_grant_ref_t);
   
   /*
    * GNTTABOP_setup_table: Set up a grant table for <dom> comprising at least
    * <nr_frames> pages. The frame addresses are written to the <frame_list>.
    * Only <nr_frames> addresses are written, even if the table is larger.
    * NOTES:
    *  1. <dom> may be specified as DOMID_SELF.
    *  2. Only a sufficiently-privileged domain may specify <dom> != DOMID_SELF.
    *  3. Xen may not support more than a single grant-table page per domain.
    */
   struct gnttab_setup_table {
       /* IN parameters. */
       domid_t  dom;
       uint32_t nr_frames;
       /* OUT parameters. */
       int16_t  status;              /* => enum grant_status */
   #if __XEN_INTERFACE_VERSION__ < 0x00040300
       XEN_GUEST_HANDLE(ulong) frame_list;
   #else
       XEN_GUEST_HANDLE(xen_pfn_t) frame_list;
   #endif
   };
   typedef struct gnttab_setup_table gnttab_setup_table_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_setup_table_t);
   
   /*
    * GNTTABOP_dump_table: Dump the contents of the grant table to the
    * xen console. Debugging use only.
    */
   struct gnttab_dump_table {
       /* IN parameters. */
       domid_t dom;
       /* OUT parameters. */
       int16_t status;               /* => enum grant_status */
   };
   typedef struct gnttab_dump_table gnttab_dump_table_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_dump_table_t);
   
   /*
    * GNTTABOP_transfer: Transfer <frame> to a foreign domain. The foreign domain
    * has previously registered its interest in the transfer via <domid, ref>.
    *
    * Note that, even if the transfer fails, the specified page no longer belongs
    * to the calling domain *unless* the error is GNTST_bad_page.
    *
    * Note further that only PV guests can use this operation.
    */
   struct gnttab_transfer {
       /* IN parameters. */
       xen_pfn_t     mfn;
       domid_t       domid;
       grant_ref_t   ref;
       /* OUT parameters. */
       int16_t       status;
   };
   typedef struct gnttab_transfer gnttab_transfer_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_transfer_t);
   
   
   /*
    * GNTTABOP_copy: Hypervisor based copy
    * source and destinations can be eithers MFNs or, for foreign domains,
    * grant references. the foreign domain has to grant read/write access
    * in its grant table.
    *
    * The flags specify what type source and destinations are (either MFN
    * or grant reference).
    *
    * Note that this can also be used to copy data between two domains
    * via a third party if the source and destination domains had previously
    * grant appropriate access to their pages to the third party.
    *
    * source_offset specifies an offset in the source frame, dest_offset
    * the offset in the target frame and  len specifies the number of
    * bytes to be copied.
    */
   
   #define _GNTCOPY_source_gref      (0)
   #define GNTCOPY_source_gref       (1<<_GNTCOPY_source_gref)
   #define _GNTCOPY_dest_gref        (1)
   #define GNTCOPY_dest_gref         (1<<_GNTCOPY_dest_gref)
   
   struct gnttab_copy {
       /* IN parameters. */
       struct gnttab_copy_ptr {
           union {
               grant_ref_t ref;
               xen_pfn_t   gmfn;
           } u;
           domid_t  domid;
           uint16_t offset;
       } source, dest;
       uint16_t      len;
       uint16_t      flags;          /* GNTCOPY_* */
       /* OUT parameters. */
       int16_t       status;
   };
   typedef struct gnttab_copy  gnttab_copy_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_copy_t);
   
   /*
    * GNTTABOP_query_size: Query the current and maximum sizes of the shared
    * grant table.
    * NOTES:
    *  1. <dom> may be specified as DOMID_SELF.
    *  2. Only a sufficiently-privileged domain may specify <dom> != DOMID_SELF.
    */
   struct gnttab_query_size {
       /* IN parameters. */
       domid_t  dom;
       /* OUT parameters. */
       uint32_t nr_frames;
       uint32_t max_nr_frames;
       int16_t  status;              /* => enum grant_status */
   };
   typedef struct gnttab_query_size gnttab_query_size_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_query_size_t);
   
   /*
    * GNTTABOP_unmap_and_replace: Destroy one or more grant-reference mappings
    * tracked by <handle> but atomically replace the page table entry with one
    * pointing to the machine address under <new_addr>.  <new_addr> will be
    * redirected to the null entry.
    * NOTES:
    *  1. The call may fail in an undefined manner if either mapping is not
    *     tracked by <handle>.
    *  2. After executing a batch of unmaps, it is guaranteed that no stale
    *     mappings will remain in the device or host TLBs.
    */
   struct gnttab_unmap_and_replace {
       /* IN parameters. */
       uint64_t host_addr;
       uint64_t new_addr;
       grant_handle_t handle;
       /* OUT parameters. */
       int16_t  status;              /* => enum grant_status */
   };
   typedef struct gnttab_unmap_and_replace gnttab_unmap_and_replace_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_unmap_and_replace_t);
   
   #if __XEN_INTERFACE_VERSION__ >= 0x0003020a
   /*
    * GNTTABOP_set_version: Request a particular version of the grant
    * table shared table structure.  This operation may be used to toggle
    * between different versions, but must be performed while no grants
    * are active.  The only defined versions are 1 and 2.
    */
   struct gnttab_set_version {
       /* IN/OUT parameters */
       uint32_t version;
   };
   typedef struct gnttab_set_version gnttab_set_version_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_set_version_t);
   
   
   /*
    * GNTTABOP_get_status_frames: Get the list of frames used to store grant
    * status for <dom>. In grant format version 2, the status is separated
    * from the other shared grant fields to allow more efficient synchronization
    * using barriers instead of atomic cmpexch operations.
    * <nr_frames> specify the size of vector <frame_list>.
    * The frame addresses are returned in the <frame_list>.
    * Only <nr_frames> addresses are returned, even if the table is larger.
    * NOTES:
    *  1. <dom> may be specified as DOMID_SELF.
    *  2. Only a sufficiently-privileged domain may specify <dom> != DOMID_SELF.
    */
   struct gnttab_get_status_frames {
       /* IN parameters. */
       uint32_t nr_frames;
       domid_t  dom;
       /* OUT parameters. */
       int16_t  status;              /* => enum grant_status */
       XEN_GUEST_HANDLE(uint64_t) frame_list;
   };
   typedef struct gnttab_get_status_frames gnttab_get_status_frames_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_get_status_frames_t);
   
   /*
    * GNTTABOP_get_version: Get the grant table version which is in
    * effect for domain <dom>.
    */
   struct gnttab_get_version {
       /* IN parameters */
       domid_t dom;
       uint16_t pad;
       /* OUT parameters */
       uint32_t version;
   };
   typedef struct gnttab_get_version gnttab_get_version_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_get_version_t);
   
   /*
    * GNTTABOP_swap_grant_ref: Swap the contents of two grant entries.
    */
   struct gnttab_swap_grant_ref {
       /* IN parameters */
       grant_ref_t ref_a;
       grant_ref_t ref_b;
       /* OUT parameters */
       int16_t status;             /* => enum grant_status */
   };
   typedef struct gnttab_swap_grant_ref gnttab_swap_grant_ref_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_swap_grant_ref_t);
   
   /*
    * Issue one or more cache maintenance operations on a portion of a
    * page granted to the calling domain by a foreign domain.
    */
   struct gnttab_cache_flush {
       union {
           uint64_t dev_bus_addr;
           grant_ref_t ref;
       } a;
       uint16_t offset; /* offset from start of grant */
       uint16_t length; /* size within the grant */
   #define GNTTAB_CACHE_CLEAN          (1u<<0)
   #define GNTTAB_CACHE_INVAL          (1u<<1)
   #define GNTTAB_CACHE_SOURCE_GREF    (1u<<31)
       uint32_t op;
   };
   typedef struct gnttab_cache_flush gnttab_cache_flush_t;
   DEFINE_XEN_GUEST_HANDLE(gnttab_cache_flush_t);
   
   #endif /* __XEN_INTERFACE_VERSION__ */
   
   /*
    * Bitfield values for gnttab_map_grant_ref.flags.
    */
    /* Map the grant entry for access by I/O devices. */
   #define _GNTMAP_device_map      (0)
   #define GNTMAP_device_map       (1<<_GNTMAP_device_map)
    /* Map the grant entry for access by host CPUs. */
   #define _GNTMAP_host_map        (1)
   #define GNTMAP_host_map         (1<<_GNTMAP_host_map)
    /* Accesses to the granted frame will be restricted to read-only access. */
   #define _GNTMAP_readonly        (2)
   #define GNTMAP_readonly         (1<<_GNTMAP_readonly)
    /*
     * GNTMAP_host_map subflag:
     *  0 => The host mapping is usable only by the guest OS.
     *  1 => The host mapping is usable by guest OS + current application.
     */
   #define _GNTMAP_application_map (3)
   #define GNTMAP_application_map  (1<<_GNTMAP_application_map)
   
    /*
     * GNTMAP_contains_pte subflag:
     *  0 => This map request contains a host virtual address.
     *  1 => This map request contains the machine addess of the PTE to update.
     */
   #define _GNTMAP_contains_pte    (4)
   #define GNTMAP_contains_pte     (1<<_GNTMAP_contains_pte)
   
   /*
    * Bits to be placed in guest kernel available PTE bits (architecture
    * dependent; only supported when XENFEAT_gnttab_map_avail_bits is set).
    */
   #define _GNTMAP_guest_avail0    (16)
   #define GNTMAP_guest_avail_mask ((uint32_t)~0 << _GNTMAP_guest_avail0)
   
   /*
    * Values for error status returns. All errors are -ve.
    */
   /* ` enum grant_status { */
   #define GNTST_okay             (0)  /* Normal return.                        */
   #define GNTST_general_error    (-1) /* General undefined error.              */
   #define GNTST_bad_domain       (-2) /* Unrecognsed domain id.                */
   #define GNTST_bad_gntref       (-3) /* Unrecognised or inappropriate gntref. */
   #define GNTST_bad_handle       (-4) /* Unrecognised or inappropriate handle. */
   #define GNTST_bad_virt_addr    (-5) /* Inappropriate virtual address to map. */
   #define GNTST_bad_dev_addr     (-6) /* Inappropriate device address to unmap.*/
   #define GNTST_no_device_space  (-7) /* Out of space in I/O MMU.              */
   #define GNTST_permission_denied (-8) /* Not enough privilege for operation.  */
   #define GNTST_bad_page         (-9) /* Specified page was invalid for op.    */
   #define GNTST_bad_copy_arg    (-10) /* copy arguments cross page boundary.   */
   #define GNTST_address_too_big (-11) /* transfer page address too large.      */
   #define GNTST_eagain          (-12) /* Operation not done; try again.        */
   #define GNTST_no_space        (-13) /* Out of space (handles etc).           */
   /* ` } */
   
   #define GNTTABOP_error_msgs {                   \
       "okay",                                     \
       "undefined error",                          \
       "unrecognised domain id",                   \
       "invalid grant reference",                  \
       "invalid mapping handle",                   \
       "invalid virtual address",                  \
       "invalid device address",                   \
       "no spare translation slot in the I/O MMU", \
       "permission denied",                        \
       "bad page",                                 \
       "copy arguments cross page boundary",       \
       "page address size too large",              \
       "operation not done; try again",            \
       "out of space",                             \
   }
   
   #endif /* __XEN_PUBLIC_GRANT_TABLE_H__ */
   
   /*
    * Local variables:
    * mode: C
    * c-file-style: "BSD"
    * c-basic-offset: 4
    * tab-width: 4
    * indent-tabs-mode: nil
    * End:
    */

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