[PATCH] Seabios - read e820 reserve from qemu_cfg

[Jes Sorensen <Jes.Sorensen@xxxxxxxxxx>]

Hi,

Right now KVM/QEMU relies on hard coded values in Seabios for the
reserved area for the TSS pages and the EPT page.

I'd like to suggest we change this to pass the value from QEMU via
qemu-cfg making it possible to move it around dynamically in the future.

Attached is a patch to Seabios for this, which defaults to the current
hard coded value if no value is provided by qemu-cfg. We can remove
the backwards compatibility later.

I'll post the QEMU patches for upstream QEMU and QEMU-KVM in a minute.

Comments most welcome!

Cheers,
Jes

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@xxxxxxxxxx>

---
 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);