[PATCH v4 5/7] 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>

---

    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_types.idl |  5 +++--
 tools/libxl/xl_cmdimpl.c    | 21 ++++++++++++++-------
 4 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index e15a49f..bfb8137 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -588,12 +588,17 @@ 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 06bbca6..13f5fe7 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_types.idl b/tools/libxl/libxl_types.idl
index 649ce50..4462586 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -169,8 +169,9 @@ 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),    # 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 4fc46eb..99a0958 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -1208,13 +1208,20 @@ 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);
+            switch(sscanf(buf, "%" SCNx64",%" SCNx64"@%" SCNx64,
+                          &b_info->iomem[i].start,
+                          &b_info->iomem[i].number,
+                          &b_info->iomem[i].gfn)) {
+                case 3: break;
+                case 2:
+                        /* default to 1:1 mapping */
+                        b_info->iomem[i].gfn = b_info->iomem[i].start;
+                        break;
+                default:
+                        fprintf(stderr,
+                                "xl: Invalid argument parsing iomem: %s\n",
+                                buf);
+                        exit(1);
             }
         }
     }
-- 
1.9.0