grant_table.h

/******************************************************************************
 * grant_table.h
 *
 * Interface for granting foreign access to page frames, and receiving
 * page-ownership transfers.
 *
 * SPDX-License-Identifier: MIT
 *
 * 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 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 purely
 * for backwards compatibility.  New guests should use version 2.
 */
#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     flags;
  /* The domain being granted foreign privileges. [GST] */
  domid_t    domid;
 
  /*
   * GTF_permit_access: Frame that @domid is allowed to map and access. [GST]
   * GTF_accept_transfer: Frame whose ownership transferred by @domid. [XEN]
   */
  UINT32     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.
 *  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]
 *  GTF_PAT, GTF_PWT, GTF_PCD: (x86) cache attribute flags for 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     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                  pad0;
    UINT64                  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                  page_off;
    UINT16                  length;
    UINT64                  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                  pad0;
    grant_ref_t             gref;
  } transitive;
 
  UINT32    __spacer[4]; /* Pad to a power of two */
};
 
typedef union grant_entry_v2 grant_entry_v2_t;
 
typedef UINT16 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,
 * `                           UINT32 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
/* ` } */
 
/*
 * Handle to track a mapping created via a grant reference.
 */
typedef UINT32 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, <handle>
 * 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            host_addr;
  UINT32            flags;      /* GNTMAP_* */
  grant_ref_t       ref;
  domid_t           dom;
  /* OUT parameters. */
  INT16             status;     /* => enum grant_status */
  grant_handle_t    handle;
  UINT64            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            host_addr;
  UINT64            dev_bus_addr;
  grant_handle_t    handle;
  /* OUT parameters. */
  INT16             status;     /* => enum grant_status */
};
 
typedef struct gnttab_unmap_grant_ref gnttab_unmap_grant_ref_t;
DEFINE_XEN_GUEST_HANDLE (gnttab_unmap_grant_ref_t);
 
/*
 * 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 address of the PTE to update.
 */
#define _GNTMAP_contains_pte  (4)
#define GNTMAP_contains_pte   (1<<_GNTMAP_contains_pte)
 
#define _GNTMAP_can_fail  (5)
#define GNTMAP_can_fail   (1<<_GNTMAP_can_fail)
 
/*
 * 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)~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)  /* Unrecognised 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 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"             \
}
 
#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:
 */