[RFC PATCH v11bis 23/26] hw/xen: Map guest XENSTORE_PFN grant in emulated Xenstore

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 hw/i386/kvm/xen_xenstore.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
index 74729cbb63..a58c89b555 100644
--- a/hw/i386/kvm/xen_xenstore.c
+++ b/hw/i386/kvm/xen_xenstore.c
@@ -21,6 +21,7 @@
 
 #include "hw/sysbus.h"
 #include "hw/xen/xen.h"
+#include "hw/xen/xen_backend_ops.h"
 #include "xen_overlay.h"
 #include "xen_evtchn.h"
 #include "xen_xenstore.h"
@@ -34,6 +35,7 @@
 
 #include "hw/xen/interface/io/xs_wire.h"
 #include "hw/xen/interface/event_channel.h"
+#include "hw/xen/interface/grant_table.h"
 
 #define TYPE_XEN_XENSTORE "xen-xenstore"
 OBJECT_DECLARE_SIMPLE_TYPE(XenXenstoreState, XEN_XENSTORE)
@@ -66,6 +68,9 @@ struct XenXenstoreState {
 
     uint8_t *impl_state;
     uint32_t impl_state_size;
+
+    struct xengntdev_handle *gt;
+    void *granted_xs;
 };
 
 struct XenXenstoreState *xen_xenstore_singleton;
@@ -1413,6 +1418,17 @@ int xen_xenstore_reset(void)
     }
     s->be_port = err;
 
+    /*
+     * We don't actually access the guest's page through the grant, because
+     * this isn't real Xen, and we can just use the page we gave it in the
+     * first place. Map the grant anyway, mostly for cosmetic purposes so
+     * it *looks* like it's in use in the guest-visible grant table.
+     */
+    s->gt = qemu_xen_gnttab_open();
+    uint32_t xs_gntref = GNTTAB_RESERVED_XENSTORE;
+    s->granted_xs = qemu_xen_gnttab_map_refs(s->gt, 1, xen_domid,
+                                             &xs_gntref, PROT_READ|PROT_WRITE);
+
     return 0;
 }
 
-- 
2.39.0