Read location and size of KVM switch area from qemu-cfg

Read location of KVM's switch area (VMX TSS pages and EPT) from QEMU
via qemu-cfg instead of relying on hard coded values.

For now, fall back to the old hard coded values for compatibility
reasons. Compatibility code can be removed in the future.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>

---
 src/paravirt.c |    9 +++++++++
 src/paravirt.h |    7 +++++++
 src/post.c     |   14 ++++++++++----
 3 files changed, 26 insertions(+), 4 deletions(-)

Index: seabios/src/paravirt.c
===================================================================
--- seabios.orig/src/paravirt.c
+++ seabios/src/paravirt.c
@@ -132,6 +132,15 @@ u16 qemu_cfg_smbios_entries(void)
     return cnt;
 }
 
+int qemu_cfg_read_e820_reserve(struct qemu_cfg_e820_reserve *reserve)
+{
+    if (!qemu_cfg_present)
+        return 0;
+
+    qemu_cfg_read((void *)reserve, sizeof(*reserve));
+    return reserve->length;
+}
+
 struct smbios_header {
     u16 length;
     u8 type;
Index: seabios/src/paravirt.h
===================================================================
--- seabios.orig/src/paravirt.h
+++ seabios/src/paravirt.h
@@ -36,6 +36,7 @@ static inline int kvm_para_available(voi
 #define QEMU_CFG_ACPI_TABLES		(QEMU_CFG_ARCH_LOCAL + 0)
 #define QEMU_CFG_SMBIOS_ENTRIES		(QEMU_CFG_ARCH_LOCAL + 1)
 #define QEMU_CFG_IRQ0_OVERRIDE		(QEMU_CFG_ARCH_LOCAL + 2)
+#define QEMU_CFG_E820_RESERVE		(QEMU_CFG_ARCH_LOCAL + 3)
 
 extern int qemu_cfg_present;
 
@@ -61,8 +62,14 @@ typedef struct QemuCfgFile {
     char name[56];
 } QemuCfgFile;
 
+struct qemu_cfg_e820_reserve {
+    u32 addr;
+    u32 length;
+};
+
 u16 qemu_cfg_first_file(QemuCfgFile *entry);
 u16 qemu_cfg_next_file(QemuCfgFile *entry);
 u32 qemu_cfg_read_file(QemuCfgFile *entry, void *dst, u32 maxlen);
+int qemu_cfg_read_e820_reserve(struct qemu_cfg_e820_reserve *reserve);
 
 #endif
Index: seabios/src/post.c
===================================================================
--- seabios.orig/src/post.c
+++ seabios/src/post.c
@@ -135,10 +135,16 @@ ram_probe(void)
              , E820_RESERVED);
     add_e820(BUILD_BIOS_ADDR, BUILD_BIOS_SIZE, E820_RESERVED);
 
-    if (kvm_para_available())
-        // 4 pages before the bios, 3 pages for vmx tss pages, the
-        // other page for EPT real mode pagetable
-        add_e820(0xfffbc000, 4*4096, E820_RESERVED);
+    if (kvm_para_available()) {
+        struct qemu_cfg_e820_reserve e820_reserve;
+        if (qemu_cfg_read_e820_reserve(&e820_reserve))
+            add_e820(e820_reserve.addr, e820_reserve.length, E820_RESERVED);
+        else {
+            // 4 pages before the bios, 3 pages for vmx tss pages, the
+            // other page for EPT real mode pagetable
+            add_e820(0xfffbc000, 4*4096, E820_RESERVED);
+        }
+    }
 
     dprintf(1, "Ram Size=0x%08x (0x%08x%08x high)\n"
             , RamSize, (u32)(RamSizeOver4G >> 32), (u32)RamSizeOver4G);