libxl,xl: add max_event_channels option to xl configuration file

Add the 'max_event_channels' option to the xl configuration file to
limit the number of event channels that domain may use.

Plumb this option through to libxl via a new libxl_build_info field
and call xc_domain_set_max_evtchn() in the post build stage of domain
creation.

A new LIBXL_HAVE_BUILDINFO_EVENT_CHANNELS #define indicates that this
new field is available.

The default value of 1023 limits the domain to using the minimum
amount of global mapping pages and at most 5 xenheap pages.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Keir Fraser <keir@xen.org>

6 files changed, 30 insertions, 0 deletions

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index cd9696934b..278dba10d8 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -580,6 +580,17 @@ Allow a guest to access specific physical IRQs.
 It is recommended to use this option only for trusted VMs under
 administrator control.
 
+=item B<max_event_channels=N>
+
+Limit the guest to using at most N event channels (PV interrupts).
+Guests use hypervisor resources for each event channel they use.
+
+The default of 1023 should be sufficient for typical guests.  The
+maximum value depends what the guest supports.  Guests supporting the
+FIFO-based event channel ABI support up to 131,071 event channels.
+Other guests are limited to 4095 (64-bit x86 and ARM) or 1023 (32-bit
+x86).
+
 =back
 
 =head2 Paravirtualised (PV) Guest Specific Options
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index c9d9535b32..1c6675d0da 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -90,6 +90,11 @@
 #define LIBXL_HAVE_BUILDINFO_HVM_VENDOR_DEVICE 1
 
 /*
+ * The libxl_domain_build_info has the event_channels field.
+ */
+#define LIBXL_HAVE_BUILDINFO_EVENT_CHANNELS 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 c5ec577127..1b320d3c92 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -208,6 +208,9 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
 
     libxl_defbool_setdefault(&b_info->disable_migrate, false);
 
+    if (!b_info->event_channels)
+        b_info->event_channels = 1023;
+
     switch (b_info->type) {
     case LIBXL_DOMAIN_TYPE_HVM:
         if (b_info->shadow_memkb == LIBXL_MEMKB_DEFAULT)
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index 6e2252afbe..356f920a6d 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -268,6 +268,13 @@ int libxl__build_post(libxl__gc *gc, uint32_t domid,
     if (rc)
         return rc;
 
+    rc = xc_domain_set_max_evtchn(ctx->xch, domid, info->event_channels);
+    if (rc) {
+        LOG(ERROR, "Failed to set event channel limit to %d (%d)",
+            info->event_channels, rc);
+        return ERROR_FAIL;
+    }
+
     libxl_cpuid_apply_policy(ctx, domid);
     if (info->cpuid != NULL)
         libxl_cpuid_set(ctx, domid, info->cpuid);
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index b5d0b70064..d2cea8a971 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -312,6 +312,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
     ("irqs",             Array(uint32, "num_irqs")),
     ("iomem",            Array(libxl_iomem_range, "num_iomem")),
     ("claim_mode",	     libxl_defbool),
+    ("event_channels",   uint32),
     ("u", KeyedUnion(None, libxl_domain_type, "type",
                 [("hvm", Struct(None, [("firmware",         string),
                                        ("bios",             libxl_bios_type),
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 14bb385f1a..a8261be048 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -845,6 +845,9 @@ static void parse_config_data(const char *config_source,
     if (!xlu_cfg_get_long (config, "videoram", &l, 0))
         b_info->video_memkb = l * 1024;
 
+    if (!xlu_cfg_get_long(config, "max_event_channels", &l, 0))
+        b_info->event_channels = l;
+
     switch(b_info->type) {
     case LIBXL_DOMAIN_TYPE_HVM:
         if (!xlu_cfg_get_string (config, "kernel", &buf, 0))