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[Xen-devel] [PATCH v7 08/10] tools/libxl: parse optional start gfn from the iomem config option

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@xxxxxxxxx>
Acked-by: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Cc: Paolo Valente <paolo.valente@xxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Eric Trudeau <etrudeau@xxxxxxxxxxxx>
Cc: Viktor Kleinik <viktor.kleinik@xxxxxxxxxxxxxxx>


        - Use LIBXL_INVALID_GFN when needed.
        - Add to the manpage a note about the mapping defaulting to 1:1 when
          the gfn parameter is not specified, and about the option being for
          auto-translated guests.
        - Remove spurious change.

        - Document what happens if the new "gfn" parameter is omitted
          while specifying the "iomem" option in the domain configuration.
        - Add LIBXL_INVALID_GFN macro with value "~(uint64_t)0".
        - Fix typo in the comment to the LIBXL_HAVE_BUILDINFO_IOMEM_START_GFN

        - 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.

        - 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        | 18 +++++++++++++-----
 tools/libxl/libxl.h          | 10 ++++++++++
 tools/libxl/libxl_create.c   |  6 ++++++
 tools/libxl/libxl_internal.h |  1 +
 tools/libxl/libxl_types.idl  |  4 ++++
 tools/libxl/xl_cmdimpl.c     | 17 ++++++++++-------
 6 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index c8ce6c1..96c2b67 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -610,12 +610,20 @@ is given in hexadecimal and may either a span e.g. 
 It is recommended to use this option only for trusted VMs under
 administrator control.
... ]>
-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.
+Allow auto-translated domains 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. B<GFN> specifies the guest frame
+number where the mapping will start in the domU's address space. If B<GFN> is
+not given, the mapping will be performed using B<IOMEM_START> as a start in the
+domU's address space, therefore performing an 1:1 mapping as default.
+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..a78944d 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -95,6 +95,16 @@
+ * LIBXL_HAVE_BUILDINFO_IOMEM_START_GFN indicates 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.
+ */
  * 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..6aa630e 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 == LIBXL_INVALID_GFN)
+            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_internal.h b/tools/libxl/libxl_internal.h
index c2b73c4..2dba844 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -91,6 +91,7 @@
 #define LIBXL_MIN_DOM0_MEM (128*1024)
+#define LIBXL_INVALID_GFN (~(uint64_t)0)
 /* use 0 as the domid of the toolstack domain for now */
 #define QEMU_SIGNATURE "DeviceModelRecord0002"
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 0f7bbf8..997cadd 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -170,8 +170,12 @@ libxl_ioport_range = Struct("ioport_range", [
 libxl_iomem_range = Struct("iomem_range", [
+    # start host frame number to be mapped to the guest
     ("start", uint64),
+    # number of frames to be mapped
     ("number", uint64),
+    # guest frame number used as a start for the mapping
+    ("gfn", uint64, {'init_val': "LIBXL_INVALID_GFN"}),
 libxl_vga_interface_info = Struct("vga_interface_info", [
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 0b38b32..9a88dcb 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) {
@@ -1213,13 +1214,15 @@ static void parse_config_data(const char *config_source,
                         "xl: Unable to get element %d in iomem list\n", i);
-            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);

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