tools/dombuilder: Fix asymmetry when setting up console and xenstore rings

libxl always uses xc_dom_gnttab_init(), which internally calls
xc_dom_gnttab{_hvm,}_seed() to set up the grants point at the console and
xenstore rings.  For HVM guests, libxl then asks Xen for the information set
up previously, and calls xc_dom_gnttab_hvm_seed() a second time, which is
wasteful.  ARM construction expects libxl to have set up
dom->{console,xenstore}_evtchn earlier, so only actually functions because of
this second call.

Rationalise everything and make it consistent for all guests.

 1) Users of the domain builder are expected to provide
    dom->{console,xenstore}_{evtchn,domid} unconditionally.  This is checked
    by setting invalid values in xc_dom_allocate(), and checking in
    xc_dom_boot_image().

 2) For x86 HVM and ARM guests, the event channels are given to Xen at the
    same time as the ring gfns.  ARM already did this, but x86 is updated to
    match.  x86 PV already provides this information in the start_info page.

 3) Libxl is updated to drop all relevant functionality from
    hvm_build_set_params(), and behave consistently with PV guests when it
    comes to the handling of dom->{console,xenstore}_{evtchn,domid,gfn}.

This removes several redundant hypercalls (including a foreign mapping) from
the x86 HVM and ARM construction paths.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Tested-by: Julien Grall <julien.grall@arm.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>

tools/libxc/include/xc_dom.h

@@ -20,6 +20,8 @@
 #include <xenguest.h>
 
 #define INVALID_PFN ((xen_pfn_t)-1)
+#define INVALID_EVTCHN (~0u)
+#define INVALID_DOMID  (~0)
 #define X86_HVM_NR_SPECIAL_PAGES    8
 #define X86_HVM_END_SPECIAL_REGION  0xff000u
 
@@ -104,10 +106,16 @@ struct xc_dom_image {
      * Details for the toolstack-prepared rings.
      *
      * *_gfn fields are allocated by the domain builder.
+     * *_{evtchn,domid} fields must be provided by the caller.
      */
     xen_pfn_t console_gfn;
     xen_pfn_t xenstore_gfn;
 
+    unsigned int console_evtchn;
+    unsigned int xenstore_evtchn;
+    uint32_t console_domid;
+    uint32_t xenstore_domid;
+
     /*
      * initrd parameters as specified in start_info page
      * Depending on capabilities of the booted kernel this may be a virtual
@@ -165,10 +173,6 @@ struct xc_dom_image {
 
     /* misc xen domain config stuff */
     unsigned long flags;
-    unsigned int console_evtchn;
-    unsigned int xenstore_evtchn;
-    uint32_t console_domid;
-    uint32_t xenstore_domid;
     xen_pfn_t shared_info_mfn;
 
     xc_interface *xch;

tools/libxc/xc_dom_arm.c

@@ -99,7 +99,7 @@ static int alloc_magic_pages(struct xc_dom_image *dom)
             dom->xenstore_gfn);
     xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_MONITOR_RING_PFN,
             base + MEMACCESS_PFN_OFFSET);
-    /* allocated by toolstack */
+
     xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_CONSOLE_EVTCHN,
             dom->console_evtchn);
     xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_STORE_EVTCHN,

tools/libxc/xc_dom_boot.c

@@ -163,6 +163,42 @@ void *xc_dom_boot_domU_map(struct xc_dom_image *dom, xen_pfn_t pfn,
     return ptr;
 }
 
+static int xc_dom_check_required_fields(struct xc_dom_image *dom)
+{
+    int rc = 0;
+
+    if ( dom->console_evtchn == INVALID_EVTCHN )
+    {
+        xc_dom_panic(dom->xch, XC_INVALID_PARAM,
+                     "%s: Caller didn't set dom->console_evtchn", __func__);
+        rc = -1;
+    }
+    if ( dom->console_domid == INVALID_DOMID )
+    {
+        xc_dom_panic(dom->xch, XC_INVALID_PARAM,
+                     "%s: Caller didn't set dom->console_domid", __func__);
+        rc = -1;
+    }
+
+    if ( dom->xenstore_evtchn == INVALID_EVTCHN )
+    {
+        xc_dom_panic(dom->xch, XC_INVALID_PARAM,
+                     "%s: Caller didn't set dom->xenstore_evtchn", __func__);
+        rc = -1;
+    }
+    if ( dom->xenstore_domid == INVALID_DOMID )
+    {
+        xc_dom_panic(dom->xch, XC_INVALID_PARAM,
+                     "%s: Caller didn't set dom->xenstore_domid", __func__);
+        rc = -1;
+    }
+
+    if ( rc )
+        errno = EINVAL;
+
+    return rc;
+}
+
 int xc_dom_boot_image(struct xc_dom_image *dom)
 {
     xc_dominfo_t info;
@@ -170,6 +206,9 @@ int xc_dom_boot_image(struct xc_dom_image *dom)
 
     DOMPRINTF_CALLED(dom->xch);
 
+    if ( (rc = xc_dom_check_required_fields(dom)) != 0 )
+        return rc;
+
     /* misc stuff*/
     if ( (rc = dom->arch_hooks->bootearly(dom)) != 0 )
         return rc;

tools/libxc/xc_dom_compat_linux.c

@@ -61,7 +61,9 @@ int xc_linux_build(xc_interface *xch, uint32_t domid,
 
     dom->flags |= flags;
     dom->console_evtchn = console_evtchn;
+    dom->console_domid = 0;
     dom->xenstore_evtchn = store_evtchn;
+    dom->xenstore_domid = 0;
 
     if ( (rc = xc_dom_boot_xen_init(dom, xch, domid)) != 0 )
         goto out;

tools/libxc/xc_dom_core.c

@@ -779,6 +779,11 @@ struct xc_dom_image *xc_dom_allocate(xc_interface *xch,
     dom->parms.elf_paddr_offset = UNSET_ADDR;
     dom->parms.p2m_base = UNSET_ADDR;
 
+    dom->console_evtchn = INVALID_EVTCHN;
+    dom->xenstore_evtchn = INVALID_EVTCHN;
+    dom->console_domid = INVALID_DOMID;
+    dom->xenstore_domid = INVALID_DOMID;
+
     dom->flags = SIF_VIRT_P2M_4TOOLS;
 
     dom->alloc_malloc += sizeof(*dom);

tools/libxc/xc_dom_x86.c

@@ -617,6 +617,8 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
     dom->xenstore_gfn = special_pfn(SPECIALPAGE_XENSTORE);
     xc_clear_domain_page(dom->xch, dom->guest_domid, dom->xenstore_gfn);
     xc_hvm_param_set(xch, domid, HVM_PARAM_STORE_PFN, dom->xenstore_gfn);
+    xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_STORE_EVTCHN,
+                     dom->xenstore_evtchn);
 
     xc_hvm_param_set(xch, domid, HVM_PARAM_BUFIOREQ_PFN,
                      special_pfn(SPECIALPAGE_BUFIOREQ));
@@ -626,6 +628,8 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
     dom->console_gfn = special_pfn(SPECIALPAGE_CONSOLE);
     xc_clear_domain_page(dom->xch, dom->guest_domid, dom->console_gfn);
     xc_hvm_param_set(xch, domid, HVM_PARAM_CONSOLE_PFN, dom->console_gfn);
+    xc_hvm_param_set(dom->xch, dom->guest_domid, HVM_PARAM_CONSOLE_EVTCHN,
+                     dom->console_evtchn);
 
     xc_hvm_param_set(xch, domid, HVM_PARAM_PAGING_RING_PFN,
                      special_pfn(SPECIALPAGE_PAGING));

tools/libxl/libxl_dom.c

@@ -862,14 +862,10 @@ out:
 }
 
 static int hvm_build_set_params(xc_interface *handle, uint32_t domid,
-                                libxl_domain_build_info *info,
-                                int store_evtchn, unsigned long *store_mfn,
-                                int console_evtchn, unsigned long *console_mfn,
-                                domid_t store_domid, domid_t console_domid)
+                                libxl_domain_build_info *info)
 {
     struct hvm_info_table *va_hvm;
     uint8_t *va_map, sum;
-    uint64_t str_mfn, cons_mfn;
     int i;
 
     if (info->type == LIBXL_DOMAIN_TYPE_HVM) {
@@ -890,15 +886,6 @@ static int hvm_build_set_params(xc_interface *handle, uint32_t domid,
         munmap(va_map, XC_PAGE_SIZE);
     }
 
-    xc_hvm_param_get(handle, domid, HVM_PARAM_STORE_PFN, &str_mfn);
-    xc_hvm_param_get(handle, domid, HVM_PARAM_CONSOLE_PFN, &cons_mfn);
-    xc_hvm_param_set(handle, domid, HVM_PARAM_STORE_EVTCHN, store_evtchn);
-    xc_hvm_param_set(handle, domid, HVM_PARAM_CONSOLE_EVTCHN, console_evtchn);
-
-    *store_mfn = str_mfn;
-    *console_mfn = cons_mfn;
-
-    xc_dom_gnttab_hvm_seed(handle, domid, *console_mfn, *store_mfn, console_domid, store_domid);
     return 0;
 }
 
@@ -1159,6 +1146,11 @@ int libxl__build_hvm(libxl__gc *gc, uint32_t domid,
 
     dom->container_type = XC_DOM_HVM_CONTAINER;
 
+    dom->console_evtchn = state->console_port;
+    dom->console_domid = state->console_domid;
+    dom->xenstore_evtchn = state->store_port;
+    dom->xenstore_domid = state->store_domid;
+
     /* The params from the configuration file are in Mb, which are then
      * multiplied by 1 Kb. This was then divided off when calling
      * the old xc_hvm_build_target_mem() which then turned them to bytes.
@@ -1263,10 +1255,7 @@ int libxl__build_hvm(libxl__gc *gc, uint32_t domid,
         goto out;
     }
 
-    rc = hvm_build_set_params(ctx->xch, domid, info, state->store_port,
-                               &state->store_mfn, state->console_port,
-                               &state->console_mfn, state->store_domid,
-                               state->console_domid);
+    rc = hvm_build_set_params(ctx->xch, domid, info);
     if (rc != 0) {
         LOG(ERROR, "hvm build set params failed");
         goto out;
@@ -1278,6 +1267,9 @@ int libxl__build_hvm(libxl__gc *gc, uint32_t domid,
         goto out;
     }
 
+    state->console_mfn = dom->console_gfn;
+    state->store_mfn = dom->xenstore_gfn;
+
     xc_dom_release(dom);
     return 0;
 

tools/libxl/libxl_internal.h

@@ -117,7 +117,6 @@
 #define STUBDOM_SPECIAL_CONSOLES 3
 #define TAP_DEVICE_SUFFIX "-emu"
 #define DOMID_XS_PATH "domid"
-#define INVALID_DOMID ~0
 
 /* Size macros. */
 #define __AC(X,Y)   (X##Y)