hw/xen: add support for Xen primary console in emulated mode

The primary console is special because the toolstack maps a page into
the guest for its ring, and also allocates the guest-side event channel.
The guest's grant table is even primed to export that page using a known
grant ref#. Add support for all that in emulated mode, so that we can
have a primary console.

For reasons unclear, the backends running under real Xen don't just use
a mapping of the well-known GNTTAB_RESERVED_CONSOLE grant ref (which
would also be in the ring-ref node in XenStore). Instead, the toolstack
sets the ring-ref node of the primary console to the GFN of the guest
page. The backend is expected to handle that special case and map it
with foreignmem operations instead.

We don't have an implementation of foreignmem ops for emulated Xen mode,
so just make it map GNTTAB_RESERVED_CONSOLE instead. This would probably
work for real Xen too, but we can't work out how to make real Xen create
a primary console of type "ioemu" to make QEMU drive it, so we can't
test that; might as well leave it as it is for now under Xen.

Now at last we can boot the Xen PV shim and run PV kernels in QEMU.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

1 files changed, 21 insertions, 2 deletions

diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index 1dc9ab0d91..c0631f9cf4 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -28,6 +28,7 @@
 #include "hw/i386/kvm/xen_overlay.h"
 #include "hw/i386/kvm/xen_evtchn.h"
 #include "hw/i386/kvm/xen_gnttab.h"
+#include "hw/i386/kvm/xen_primary_console.h"
 #include "hw/i386/kvm/xen_xenstore.h"
 
 #include "hw/xen/interface/version.h"
@@ -182,7 +183,8 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
         return ret;
     }
 
-    /* The page couldn't be overlaid until KVM was initialized */
+    /* The pages couldn't be overlaid until KVM was initialized */
+    xen_primary_console_reset();
     xen_xenstore_reset();
 
     return 0;
@@ -812,11 +814,23 @@ static bool handle_get_param(struct kvm_xen_exit *exit, X86CPU *cpu,
     case HVM_PARAM_STORE_EVTCHN:
         hp.value = xen_xenstore_get_port();
         break;
+    case HVM_PARAM_CONSOLE_PFN:
+        hp.value = xen_primary_console_get_pfn();
+        if (!hp.value) {
+            err = -EINVAL;
+        }
+        break;
+    case HVM_PARAM_CONSOLE_EVTCHN:
+        hp.value = xen_primary_console_get_port();
+        if (!hp.value) {
+            err = -EINVAL;
+        }
+        break;
     default:
         return false;
     }
 
-    if (kvm_copy_to_gva(cs, arg, &hp, sizeof(hp))) {
+    if (!err && kvm_copy_to_gva(cs, arg, &hp, sizeof(hp))) {
         err = -EFAULT;
     }
 out:
@@ -1427,6 +1441,11 @@ int kvm_xen_soft_reset(void)
         return err;
     }
 
+    err = xen_primary_console_reset();
+    if (err) {
+        return err;
+    }
+
     err = xen_xenstore_reset();
     if (err) {
         return err;