[Xen-devel] [PATCH 14/24] xenstored: use grant references instead of map_foreign_range

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

From: Alex Zeffertt <alex.zeffertt@xxxxxxxxxxxxx>

make xenstored use grantref rather than map_foreign_range (which can
only be used by privileged domains)

This patch modifies the xenstore daemon to use xc_gnttab_map_grant_ref
instead of xc_map_foreign_range where available.

Previous versions of this patch have been sent to xen-devel. See
http://lists.xensource.com/archives/html/xen-devel/2008-07/msg00610.html
http://lists.xensource.com/archives/html/xen-devel/2009-03/msg01492.html

Signed-off-by: Diego Ongaro <diego.ongaro@xxxxxxxxxx>
Signed-off-by: Alex Zeffertt <alex.zeffertt@xxxxxxxxxxxxx>
Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 tools/xenstore/xenstored_domain.c |   54 ++++++++++++++++++++++++++++++++----
 1 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/tools/xenstore/xenstored_domain.c 
b/tools/xenstore/xenstored_domain.c
index 443af82..c521e52 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -32,8 +32,10 @@
 #include "xenstored_watch.h"
 
 #include <xenctrl.h>
+#include <xen/grant_table.h>
 
 static xc_interface **xc_handle;
+static xc_gnttab **xcg_handle;
 static evtchn_port_t virq_port;
 
 xc_evtchn *xce_handle = NULL;
@@ -163,6 +165,26 @@ static int readchn(struct connection *conn, void *data, 
unsigned int len)
        return len;
 }
 
+static void *map_interface(domid_t domid, unsigned long mfn)
+{
+       if (*xcg_handle >= 0) {
+               /* this is the preferred method */
+               return xc_gnttab_map_grant_ref(*xcg_handle, domid,
+                       GNTTAB_RESERVED_XENSTORE, PROT_READ|PROT_WRITE);
+       } else {
+               return xc_map_foreign_range(*xc_handle, domid,
+                       getpagesize(), PROT_READ|PROT_WRITE, mfn);
+       }
+}
+
+static void unmap_interface(void *interface)
+{
+       if (*xcg_handle >= 0)
+               xc_gnttab_munmap(*xcg_handle, interface, 1);
+       else
+               munmap(interface, getpagesize());
+}
+
 static int destroy_domain(void *_domain)
 {
        struct domain *domain = _domain;
@@ -174,8 +196,14 @@ static int destroy_domain(void *_domain)
                        eprintf("> Unbinding port %i failed!\n", domain->port);
        }
 
-       if (domain->interface)
-               munmap(domain->interface, getpagesize());
+       if (domain->interface) {
+               /* Domain 0 was mapped by dom0_init, so it must be unmapped
+                  using munmap() and not the grant unmap call. */
+               if (domain->domid == 0)
+                       munmap(domain->interface, getpagesize());
+               else
+                       unmap_interface(domain->interface);
+       }
 
        fire_watches(NULL, "@releaseDomain", false);
 
@@ -344,9 +372,7 @@ void do_introduce(struct connection *conn, struct 
buffered_data *in)
        domain = find_domain_by_domid(domid);
 
        if (domain == NULL) {
-               interface = xc_map_foreign_range(
-                       *xc_handle, domid,
-                       getpagesize(), PROT_READ|PROT_WRITE, mfn);
+               interface = map_interface(domid, mfn);
                if (!interface) {
                        send_error(conn, errno);
                        return;
@@ -354,7 +380,7 @@ void do_introduce(struct connection *conn, struct 
buffered_data *in)
                /* Hang domain off "in" until we're finished. */
                domain = new_domain(in, domid, port);
                if (!domain) {
-                       munmap(interface, getpagesize());
+                       unmap_interface(interface);
                        send_error(conn, errno);
                        return;
                }
@@ -552,6 +578,12 @@ static int close_xc_handle(void *_handle)
        return 0;
 }
 
+static int close_xcg_handle(void *_handle)
+{
+       xc_gnttab_close(*(xc_gnttab **)_handle);
+       return 0;
+}
+
 /* Returns the implicit path of a connection (only domains have this) */
 const char *get_implicit_path(const struct connection *conn)
 {
@@ -603,6 +635,16 @@ void domain_init(void)
 
        talloc_set_destructor(xc_handle, close_xc_handle);
 
+       xcg_handle = talloc(talloc_autofree_context(), xc_gnttab*);
+       if (!xcg_handle)
+               barf_perror("Failed to allocate domain gnttab handle");
+
+       *xcg_handle = xc_gnttab_open(NULL, 0);
+       if (*xcg_handle < 0)
+               xprintf("WARNING: Failed to open connection to gnttab\n");
+       else
+               talloc_set_destructor(xcg_handle, close_xcg_handle);
+
        xce_handle = xc_evtchn_open(NULL, 0);
 
        if (xce_handle == NULL)
-- 
1.7.7.6


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