[RFC PATCH 8/9] pc: adjust e820 map on hot-add and hot-remove

[Vasilis Liaskovitis]

Hotplugged memory is not persistent in the e820 memory maps. After hotplugging
 a memslot and rebooting the VM, the hotplugged device is not present.

A possible solution is to add an e820 for the new memslot in the acpi_piix4
 hot-add handler. On a reset, Seabios (see next patch in series) will enable all
 memory devices for which it finds an e820 entry that covers the devices's address
 range.

On hot-remove, the acpi_piix4 handler will try to remove the e820 entry
 corresponding to the device. This will work when no VM reboots happen
 between hot-add and hot-remove, but it is not a sufficient solution in
 general: Seabios and GuestOS merge adjacent e820 entries on machine reboot,
 so the sequence hot-add/ rebootVM / hot-remove will fail to remove a
 corresponding e820 entry at the hot-remove phase.

Signed-off-by: Vasilis Liaskovitis 
---
 hw/acpi_piix4.c |    6 ++++++
 hw/pc.c         |   28 ++++++++++++++++++++++++++++
 hw/pc.h         |    1 +
 3 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
index 2921d18..2b5fd04 100644
--- a/hw/acpi_piix4.c
+++ b/hw/acpi_piix4.c
@@ -619,6 +619,9 @@ static void piix4_memslot_eject(uint32_t addr, uint32_t val)
             s = memslot_find_from_idx(start + idx);
             assert(s != NULL);
             memslot_depopulate(s);
+            if (e820_del_entry(s->start, s->size, E820_RAM) == -EBUSY)
+                PIIX4_DPRINTF("failed to remove e820 entry for memslot %u\n",
+                       s->idx);
         }
         val = val >> 1;
         idx++;
@@ -634,6 +637,9 @@ static int piix4_memslot_hotplug(DeviceState *qdev, SysBusDevice *dev, int

if (add) {
         enable_mem_device(s, slot->idx);
+        if (e820_add_entry(slot->start, slot->size, E820_RAM) == -EBUSY)
+            PIIX4_DPRINTF("failed to add e820 entry for memslot %u\n",
+                    slot->idx);
     }
     else {
         disable_mem_device(s, slot->idx);
diff --git a/hw/pc.c b/hw/pc.c
index f1f550a..04d243f 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -593,6 +593,34 @@ int e820_add_entry(uint64_t address, uint64_t length, uint32_t type)
     return index;
 }

+int e820_del_entry(uint64_t address, uint64_t length, uint32_t type)
+{
+    int index = le32_to_cpu(e820_table.count);
+    int search;
+    struct e820_entry *entry;
+
+    if (index == 0)
+        return -EBUSY;
+    search = index - 1;
+    entry = &e820_table.entry[search];
+    while (search >= 0) {
+        if ((entry->address == cpu_to_le64(address)) &&
+                (entry->length == cpu_to_le64(length)) &&
+                (entry->type == cpu_to_le32(type))){
+            if (search != index - 1) {
+                memcpy(&e820_table.entry[search], &e820_table.entry[search + 1],
+                        sizeof(struct e820_entry) * (index - search));
+            }
+            index--;
+            e820_table.count = cpu_to_le32(index);
+            return 1;
+        }
+        search--;
+        entry = &e820_table.entry[search];
+    }
+    return -EBUSY;
+}
+
 static void bochs_bios_setup_hp_memslots(uint64_t *fw_cfg_slots);

static void *bochs_bios_init(void)
diff --git a/hw/pc.h b/hw/pc.h
index 74d3369..4925e8c 100644
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -226,5 +226,6 @@ void pc_system_firmware_init(MemoryRegion *rom_memory);
 #define E820_UNUSABLE   5

int e820_add_entry(uint64_t, uint64_t, uint32_t);
+int e820_del_entry(uint64_t, uint64_t, uint32_t);

#endif