[RFC PATCH v5 48/52] i386/xen: Reserve Xen special pages for console, xenstore rings

[David Woodhouse <dwmw2@infradead.org>]

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

Xen has eight frames at 0xfeff8000 for this; we only really need two for
now and KVM puts the identity map at 0xfeffc000, so limit ourselves to
four.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 include/sysemu/kvm_xen.h  |  8 ++++++++
 target/i386/kvm/xen-emu.c | 15 +++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/sysemu/kvm_xen.h b/include/sysemu/kvm_xen.h
index 4999a0cff4..6e374a06ee 100644
--- a/include/sysemu/kvm_xen.h
+++ b/include/sysemu/kvm_xen.h
@@ -25,4 +25,12 @@ uint16_t kvm_xen_get_gnttab_max_frames(void);
 #define kvm_xen_has_cap(cap) (!!(kvm_xen_get_caps() &           \
                                  KVM_XEN_HVM_CONFIG_ ## cap))
 
+#define XEN_SPECIAL_AREA_ADDR 0xfeff8000UL
+#define XEN_SPECIAL_AREA_SIZE 0x4000UL
+
+#define XEN_SPECIALPAGE_CONSOLE     0
+#define XEN_SPECIALPAGE_XENSTORE    1
+
+#define XEN_SPECIAL_PFN(x) ((XEN_SPECIAL_AREA_ADDR >> TARGET_PAGE_BITS) + XEN_SPECIALPAGE_##x)
+
 #endif /* QEMU_SYSEMU_KVM_XEN_H */
diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index 7f13ae6a8b..83ab96724e 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -24,6 +24,7 @@
 
 #include "hw/pci/msi.h"
 #include "hw/i386/apic-msidef.h"
+#include "hw/i386/e820_memory_layout.h"
 #include "hw/i386/kvm/xen_overlay.h"
 #include "hw/i386/kvm/xen_evtchn.h"
 #include "hw/i386/kvm/xen_gnttab.h"
@@ -137,7 +138,21 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
         return ret;
     }
 
+    /* If called a second time, don't repeat the rest of the setup. */
+    if (s->xen_caps) {
+        return 0;
+    }
+
     s->xen_caps = xen_caps;
+
+    /* Tell fw_cfg to notify the BIOS to reserve the range. */
+    ret = e820_add_entry(XEN_SPECIAL_AREA_ADDR, XEN_SPECIAL_AREA_SIZE,
+                         E820_RESERVED);
+    if (ret < 0) {
+        fprintf(stderr, "e820_add_entry() table is full\n");
+        return ret;
+    }
+
     return 0;
 }
 
-- 
2.35.3