[PATCH v5 6/8] tools, libxl: parse optional start gfn from the iomem config option

[Arianna Avanzini <avanzini.arianna@gmail.com>]

Currently, the "iomem" domU config option allows to specify a machine
address range to be mapped to the domU. However, there is no way to
specify the guest address range used for the mapping. This commit
extends the iomem option handling code to parse an additional, optional
parameter: this parameter, if given, specifies the start guest address
used for the mapping; if no start guest address is given, a 1:1 mapping
is performed as default.

Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Cc: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Paolo Valente <paolo.valente@unimore.it>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Julien Grall <julien.grall@citrix.com>
Cc: Ian Campbell <Ian.Campbell@eu.citrix.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Eric Trudeau <etrudeau@broadcom.com>
Cc: Viktor Kleinik <viktor.kleinik@globallogic.com>

---

    v5:
        - Initialize the gfn field of the iomem structure with the
          value "(uint64_t)-1".
        - Defer the assignment of the value of "start" to "gfn", if
          "gfn" has been initialized to the default value, in libxl.
        - Use a local variable to keep the return value of sscanf()
          for better code readability.

    v4:
        - Add definition of a LIBXL_HAVE_BUILDINFO_IOMEM_START_GFN macro
          to indicate the availability of the new option.
        - Simplify the code parsing the new optional parameter by using
          the switch construct on the return value of the sscanf() function
          instead of calling the function twice.
        - Add a short paragraph to the manpage about the use of the iomem
          option to passthrough devices protected by an IOMMU.
        - Add comments to the fields of the "iomem" structure.

---
 docs/man/xl.cfg.pod.5       | 13 +++++++++----
 tools/libxl/libxl.h         | 10 ++++++++++
 tools/libxl/libxl_create.c  |  6 ++++++
 tools/libxl/libxl_types.idl |  7 +++++--
 tools/libxl/xl_cmdimpl.c    | 19 ++++++++++---------
 5 files changed, 40 insertions(+), 15 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index a6663b9..d54f601 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -602,12 +602,17 @@ is given in hexadecimal and may either a span e.g. C<2f8-2ff>
 It is recommended to use this option only for trusted VMs under
 administrator control.
 
-=item B<iomem=[ "IOMEM_START,NUM_PAGES", "IOMEM_START,NUM_PAGES", ... ]>
+=item B<iomem=[ "IOMEM_START,NUM_PAGES[@GFN]", "IOMEM_START,NUM_PAGES[@GFN]", ... ]>
 
 Allow guest to access specific hardware I/O memory pages. B<IOMEM_START>
-is a physical page number. B<NUM_PAGES> is the number
-of pages beginning with B<START_PAGE> to allow access. Both values
-must be given in hexadecimal.
+is a physical page number. B<NUM_PAGES> is the number of pages beginning
+with B<START_PAGE> to allow access. B<GFN> specifies the guest frame number
+where the mapping will start in the domU's address space.
+All of these values must be given in hexadecimal.
+
+Note that the IOMMU won't be updated with the mappings specified with this
+option. This option therefore should not be used to passthrough any
+IOMMU-protected device.
 
 It is recommended to use this option only for trusted VMs under
 administrator control.
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index b2c3015..e4a1128 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -95,6 +95,16 @@
 #define LIBXL_HAVE_BUILDINFO_EVENT_CHANNELS 1
 
 /*
+ * LIBXL_HAVE_BUILDINFO_IOMEM_START_GFN indicated that it is possible
+ * to specify the start guest frame number used to map a range of I/O
+ * memory machine frame numbers via the 'gfn' field (of type uint64)
+ * of the 'iomem' structure. An array of iomem structures is embedded
+ * in libxl_domain_build_info and used to map the indicated memory
+ * ranges during domain build.
+ */
+#define LIBXL_HAVE_BUILDINFO_IOMEM_START_GFN 1
+
+/*
  * libxl ABI compatibility
  *
  * The only guarantee which libxl makes regarding ABI compatibility
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index d015cf4..369cd77 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -102,6 +102,8 @@ static int sched_params_valid(libxl__gc *gc,
 int libxl__domain_build_info_setdefault(libxl__gc *gc,
                                         libxl_domain_build_info *b_info)
 {
+    int i;
+
     if (b_info->type != LIBXL_DOMAIN_TYPE_HVM &&
         b_info->type != LIBXL_DOMAIN_TYPE_PV)
         return ERROR_INVAL;
@@ -212,6 +214,10 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
 
     libxl_defbool_setdefault(&b_info->disable_migrate, false);
 
+    for (i = 0 ; i < b_info->num_iomem; i++)
+        if (b_info->iomem[i].gfn == (uint64_t)-1)
+            b_info->iomem[i].gfn = b_info->iomem[i].start;
+
     if (!b_info->event_channels)
         b_info->event_channels = 1023;
 
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 612645c..69f8ea3 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -170,8 +170,11 @@ libxl_ioport_range = Struct("ioport_range", [
     ])
 
 libxl_iomem_range = Struct("iomem_range", [
-    ("start", uint64),
-    ("number", uint64),
+    ("start", uint64),                 # start host frame number to be mapped
+                                       # to the guest
+    ("number", uint64),                # number of frames to be mapped
+    ("gfn", uint64, {'init_val': -1}), # guest frame number used as a start
+                                       # for the mapping
     ])
 
 libxl_vga_interface_info = Struct("vga_interface_info", [
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 8389468..10df96c 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -1200,6 +1200,7 @@ static void parse_config_data(const char *config_source,
     }
 
     if (!xlu_cfg_get_list(config, "iomem", &iomem, &num_iomem, 0)) {
+        int ret;
         b_info->num_iomem = num_iomem;
         b_info->iomem = calloc(num_iomem, sizeof(*b_info->iomem));
         if (b_info->iomem == NULL) {
@@ -1213,19 +1214,19 @@ static void parse_config_data(const char *config_source,
                         "xl: Unable to get element %d in iomem list\n", i);
                 exit(1);
             }
-            if(sscanf(buf, "%" SCNx64",%" SCNx64,
-                     &b_info->iomem[i].start,
-                     &b_info->iomem[i].number)
-                  != 2) {
-               fprintf(stderr,
-                       "xl: Invalid argument parsing iomem: %s\n", buf);
-               exit(1);
+            libxl_iomem_range_init(&b_info->iomem[i]);
+            ret = sscanf(buf, "%" SCNx64",%" SCNx64"@%" SCNx64,
+                         &b_info->iomem[i].start,
+                         &b_info->iomem[i].number,
+                         &b_info->iomem[i].gfn);
+            if (ret < 2) {
+                fprintf(stderr,
+                        "xl: Invalid argument parsing iomem: %s\n", buf);
+                exit(1);
             }
         }
     }
 
-
-
     if (!xlu_cfg_get_list (config, "disk", &vbds, 0, 0)) {
         d_config->num_disks = 0;
         d_config->disks = NULL;
-- 
1.9.1