[xen] Use version 1 grant tables by default

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).

Note that the use of version 1 tables on a 64-bit system introduces a
possible failure path in which a frame number cannot fit into the
32-bit field within the v1 structure.  This in turn introduces
additional failure paths into netfront_transmit() and
netfront_refill_rx().

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 120 insertions, 17 deletions

diff --git a/src/interface/xen/xengrant.c b/src/interface/xen/xengrant.c
index 55731bfa..be12b23d 100644
--- a/src/interface/xen/xengrant.c
+++ b/src/interface/xen/xengrant.c
@@ -20,6 +20,7 @@
 FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <stdint.h>
+#include <strings.h>
 #include <errno.h>
 #include <assert.h>
 #include <ipxe/io.h>
@@ -32,6 +33,106 @@ FILE_LICENCE ( GPL2_OR_LATER );
  *
  */
 
+/** 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).
+ */
+#define XENGRANT_TRY_VERSION 1
+
+/**
+ * Initialise grant table
+ *
+ * @v xen		Xen hypervisor
+ * @ret rc		Return status code
+ */
+int xengrant_init ( struct xen_hypervisor *xen ) {
+	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;
+}
+
 /**
  * Allocate grant references
  *
@@ -42,22 +143,22 @@ FILE_LICENCE ( GPL2_OR_LATER );
  */
 int xengrant_alloc ( struct xen_hypervisor *xen, grant_ref_t *refs,
 		     unsigned int count ) {
-	union grant_entry_v2 *entry;
-	unsigned int mask = ( xen->grant.count - 1 );
+	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 = ( xen->grant.count - xen->grant.used -
-		  GNTTAB_NR_RESERVED_ENTRIES );
+	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, xen->grant.count );
+		       "of %d available)\n", count, avail, entries );
 		return -ENOBUFS;
 	}
 	DBGC ( xen, "XENGRANT allocating %d references (from %d of %d "
-	       "available)\n", count, avail, xen->grant.count );
+	       "available)\n", count, avail, entries );
 
 	/* Update number of references used */
 	xen->grant.used += count;
@@ -66,24 +167,27 @@ int xengrant_alloc ( struct xen_hypervisor *xen, grant_ref_t *refs,
 	for ( ref = xen->grant.ref ; count ; ref = ( ( ref + 1 ) & mask ) ) {
 
 		/* Sanity check */
-		assert ( check++ < xen->grant.count );
+		assert ( check++ < entries );
 
 		/* Skip reserved references */
 		if ( ref < GNTTAB_NR_RESERVED_ENTRIES )
 			continue;
 
 		/* Skip in-use references */
-		entry = &xen->grant.table[ref];
-		if ( readw ( &entry->hdr.flags ) & GTF_type_mask )
+		hdr = xengrant_header ( xen, ref );
+		if ( readw ( &hdr->flags ) & GTF_type_mask )
 			continue;
-		if ( readw ( &entry->hdr.domid ) == DOMID_SELF )
+		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, &entry->hdr.domid );
+		writew ( DOMID_SELF, &hdr->domid );
 		DBGC2 ( xen, "XENGRANT allocated ref %d\n", ref );
 
 		/* Record reference */
@@ -105,7 +209,7 @@ int xengrant_alloc ( struct xen_hypervisor *xen, grant_ref_t *refs,
  */
 void xengrant_free ( struct xen_hypervisor *xen, grant_ref_t *refs,
 		     unsigned int count ) {
-	union grant_entry_v2 *entry;
+	struct grant_entry_header *hdr;
 	unsigned int ref;
 	unsigned int i;
 
@@ -114,12 +218,11 @@ void xengrant_free ( struct xen_hypervisor *xen, grant_ref_t *refs,
 
 		/* Sanity check */
 		ref = refs[i];
-		assert ( ref < xen->grant.count );
+		assert ( ref < xengrant_entries ( xen ) );
 
-		/* Mark reference as unused */
-		entry = &xen->grant.table[ref];
-		writew ( 0, &entry->hdr.flags );
-		writew ( 0, &entry->hdr.domid );
+		/* Zero reference */
+		hdr = xengrant_header ( xen, ref );
+		xengrant_zero ( xen, hdr );
 		DBGC2 ( xen, "XENGRANT freed ref %d\n", ref );
 	}
 }