include/public/grant_table.h - arch-x86_32 - Xen public headers

    /* SPDX-License-Identifier: MIT */
    /******************************************************************************
     * grant_table.h
     *
     * Interface for granting foreign access to page frames, and receiving
     * page-ownership transfers.
     *
     * 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)
     * ` [see __HYPERVISOR_grant_table_op]
     * `
     *
     * @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);
    /* [see GNTTABOP_map_grant_ref] */

    /*
     * 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);
    /* [see GNTTABOP_unmap_grant_ref] */

    /*
     * 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);
    /* [see GNTTABOP_setup_table] */

    /*
     * 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);
    /* [see GNTTABOP_dump_table] */

    /*
     * 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);
    /* [see GNTTABOP_transfer] */

    /*
     * 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);
    /* [see GNTTABOP_copy] */

    /*
     * 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);
    /* [see GNTTABOP_query_size] */

    /*
     * 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);
    /* [see GNTTABOP_unmap_and_replace] */

    #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);
    /* [see GNTTABOP_set_version] */

    /*
     * 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);
    /* [see GNTTABOP_get_status_frames] */

    /*
     * 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);
    /* [see GNTTABOP_get_version] */

    /*
     * 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);
    /* [see GNTTABOP_swap_grant_ref] */

    /*
     * 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);
    /* [see GNTTABOP_cache_flush] */

    #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:
     */