xengrant.c File Reference

Xen grant tables. More...

#include <stdint.h>
#include <strings.h>
#include <errno.h>
#include <assert.h>
#include <ipxe/io.h>
#include <ipxe/xen.h>
#include <ipxe/xengrant.h>

Go to the source code of this file.

Macros
#define	XENGRANT_TRY_VERSION   1
	Grant table version to try setting. More...

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
	FILE_SECBOOT (PERMITTED)
int	xengrant_init (struct xen_hypervisor *xen)
	Initialise grant table. More...
int	xengrant_alloc (struct xen_hypervisor *xen, grant_ref_t *refs, unsigned int count)
	Allocate grant references. More...
void	xengrant_free (struct xen_hypervisor *xen, grant_ref_t *refs, unsigned int count)
	Free grant references. More...

Detailed Description

Xen grant tables.

Definition in file xengrant.c.

Macro Definition Documentation

XENGRANT_TRY_VERSION

#define XENGRANT_TRY_VERSION   1

Grant table version to try setting.

Using version 1 grant tables limits guests to using 16TB of grantable RAM, and prevents the use of subpage grants. Some versions of the Xen hypervisor refuse to allow the grant table version to be set after the first grant references have been created, so the loaded operating system may be stuck with whatever choice we make here. We therefore currently use version 2 grant tables, since they give the most flexibility to the loaded OS.

Current versions (7.2.0) of the Windows PV drivers have no support for version 2 grant tables, and will merrily create version 1 entries in what the hypervisor believes to be a version 2 table. This causes some confusion.

Avoid this problem by attempting to use version 1 tables, since otherwise we may render Windows unable to boot.

Play nicely with other potential bootloaders by accepting either version 1 or version 2 grant tables (if we are unable to set our requested version).

Definition at line 63 of file xengrant.c.

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER_OR_UBDL

)

FILE_SECBOOT()

FILE_SECBOOT

(

PERMITTED

)

xengrant_init()

int xengrant_init

(

struct xen_hypervisor *

xen

)

Initialise grant table.

Parameters

xen	Xen hypervisor

Return values

rc	Return status code

Definition at line 71 of file xengrant.c.

                                                 {
        struct gnttab_query_size size;
        struct gnttab_set_version set_version;
        struct gnttab_get_version get_version;
        struct grant_entry_v1 *v1;
        union grant_entry_v2 *v2;
        unsigned int version;
        int xenrc;
        int rc;

        /* Get grant table size */
        size.dom = DOMID_SELF;
        if ( ( xenrc = xengrant_query_size ( xen, &size ) ) != 0 ) {
                rc = -EXEN ( xenrc );
                DBGC ( xen, "XENGRANT could not get table size: %s\n",
                       strerror ( rc ) );
                return rc;
        }
        xen->grant.len = ( size.nr_frames * PAGE_SIZE );

        /* Set grant table version, if applicable */
        set_version.version = XENGRANT_TRY_VERSION;
        if ( ( xenrc = xengrant_set_version ( xen, &set_version ) ) != 0 ) {
                rc = -EXEN ( xenrc );
                DBGC ( xen, "XENGRANT could not set version %d: %s\n",
                       XENGRANT_TRY_VERSION, strerror ( rc ) );
                /* Continue; use whatever version is current */
        }

        /* Get grant table version */
        get_version.dom = DOMID_SELF;
        get_version.pad = 0;
        if ( ( xenrc = xengrant_get_version ( xen, &get_version ) ) == 0 ) {
                version = get_version.version;
                switch ( version ) {

                case 0:
                        /* Version not yet specified: will be version 1 */
                        version = 1;
                        break;

                case 1 :
                        /* Version 1 table: nothing special to do */
                        break;

                case 2:
                        /* Version 2 table: configure shift appropriately */
                        xen->grant.shift = ( fls ( sizeof ( *v2 ) /
                                                   sizeof ( *v1 ) ) - 1 );
                        break;

                default:
                        /* Unsupported version */
                        DBGC ( xen, "XENGRANT detected unsupported version "
                               "%d\n", version );
                        return -ENOTSUP;

                }
        } else {
                rc = -EXEN ( xenrc );
                DBGC ( xen, "XENGRANT could not get version (assuming v1): "
                       "%s\n", strerror ( rc ) );
                version = 1;
        }

        DBGC ( xen, "XENGRANT using v%d table with %d entries\n",
               version, xengrant_entries ( xen ) );
        return 0;
}

References DBGC, DOMID_SELF, ENOTSUP, EXEN, fls, xen_hypervisor::grant, xen_grant::len, PAGE_SIZE, rc, xen_grant::shift, size, strerror(), v1, v2, version, and XENGRANT_TRY_VERSION.

Referenced by hvm_map_grant().

xengrant_alloc()

int xengrant_alloc	(	struct xen_hypervisor *	xen,
		grant_ref_t *	refs,
		unsigned int	count
	)

Allocate grant references.

Parameters

xen	Xen hypervisor
refs	Grant references to fill in
count	Number of references

Return values

rc	Return status code

Definition at line 149 of file xengrant.c.

                                          {
        struct grant_entry_header *hdr;
        unsigned int entries = xengrant_entries ( xen );
        unsigned int mask = ( entries - 1 );
        unsigned int check = 0;
        unsigned int avail;
        unsigned int ref;

        /* Fail unless we have enough references available */
        avail = ( entries - xen->grant.used - GNTTAB_NR_RESERVED_ENTRIES );
        if ( avail < count ) {
                DBGC ( xen, "XENGRANT cannot allocate %d references (only %d "
                       "of %d available)\n", count, avail, entries );
                return -ENOBUFS;
        }
        DBGC ( xen, "XENGRANT allocating %d references (from %d of %d "
               "available)\n", count, avail, entries );

        /* Update number of references used */
        xen->grant.used += count;

        /* Find unused references */
        for ( ref = xen->grant.ref ; count ; ref = ( ( ref + 1 ) & mask ) ) {

                /* Sanity check */
                assert ( check++ < entries );

                /* Skip reserved references */
                if ( ref < GNTTAB_NR_RESERVED_ENTRIES )
                        continue;

                /* Skip in-use references */
                hdr = xengrant_header ( xen, ref );
                if ( readw ( &hdr->flags ) & GTF_type_mask )
                        continue;
                if ( readw ( &hdr->domid ) == DOMID_SELF )
                        continue;

                /* Zero reference */
                xengrant_zero ( xen, hdr );

                /* Mark reference as in-use.  We leave the flags as
                 * empty (to avoid creating a valid grant table entry)
                 * and set the domid to DOMID_SELF.
                 */
                writew ( DOMID_SELF, &hdr->domid );
                DBGC2 ( xen, "XENGRANT allocated ref %d\n", ref );

                /* Record reference */
                refs[--count] = ref;
        }

        /* Update cursor */
        xen->grant.ref = ref;

        return 0;
}

References assert(), count, DBGC, DBGC2, DOMID_SELF, ENOBUFS, GNTTAB_NR_RESERVED_ENTRIES, xen_hypervisor::grant, GTF_type_mask, hdr, readw(), xen_grant::ref, ref, refs, xen_grant::used, writew, and xengrant_zero().

Referenced by netfront_probe().

xengrant_free()

void xengrant_free	(	struct xen_hypervisor *	xen,
		grant_ref_t *	refs,
		unsigned int	count
	)

Free grant references.

Parameters

xen	Xen hypervisor
refs	Grant references
count	Number of references

Definition at line 215 of file xengrant.c.

                                          {
        struct grant_entry_header *hdr;
        unsigned int ref;
        unsigned int i;

        /* Free references */
        for ( i = 0 ; i < count ; i++ ) {

                /* Sanity check */
                ref = refs[i];
                assert ( ref < xengrant_entries ( xen ) );

                /* Zero reference */
                hdr = xengrant_header ( xen, ref );
                xengrant_zero ( xen, hdr );
                DBGC2 ( xen, "XENGRANT freed ref %d\n", ref );
        }
}

References assert(), count, DBGC2, hdr, ref, refs, and xengrant_zero().

Referenced by netfront_probe(), and netfront_remove().