grant_table.h

xen 3.2.2 源码

/******************************************************************************
 * 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__


/***********************************
 * 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 (arch/xen/kernel/grant_table.c).
 * 
 * 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.
 */

/*
 * 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.
 */
struct grant_entry {
    /* 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: Frame that @domid is allowed to map and access. [GST]
     * GTF_accept_transfer: Frame whose ownership transferred by @domid. [XEN]
     */
    uint32_t frame;
};
typedef struct grant_entry grant_entry_t;

/*
 * 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.
 */
#define GTF_invalid         (0U<<0)
#define GTF_permit_access   (1U<<0)
#define GTF_accept_transfer (2U<<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]
 */
#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)

/*
 * 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)


/***********************************
 * GRANT TABLE QUERIES AND USES
 */

/*
 * Reference to a grant entry in a specified domain's grant table.
 */
typedef uint32_t grant_ref_t;

/*
 * 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, <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!
 */
#define GNTTABOP_map_grant_ref        0
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;              /* GNTST_* */
    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.
 */
#define GNTTABOP_unmap_grant_ref      1
struct gnttab_unmap_grant_ref {
    /* IN parameters. */
    uint64_t host_addr;
    uint64_t dev_bus_addr;
    grant_handle_t handle;
    /* OUT parameters. */