/****************************************************************************** * 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 (,) for access * by devices and/or host CPUs. If successful, is a tracking number * that must be presented later to destroy the mapping(s). On error, * is a negative status code. * NOTES: * 1. If GNTMAP_device_map is specified then 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 . * 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 . If or is zero, that * field is ignored. If non-zero, they must refer to a device/host mapping * that is tracked by * NOTES: * 1. The call may fail in an undefined manner if either mapping is not * tracked by . * 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: */