[6/7] hw/smbios: fix overlapping table handle numbers with large memory vms

Commit Message

Ani Sinha Feb. 23, 2022, 2:33 p.m. UTC

The current smbios table implementation splits the main memory in 16 GiB
(DIMM like) chunks. With the current smbios table assignment code, we can have
only 512 such chunks before the 16 bit handle numbers in the header for tables
17 and 19 conflict. A guest with more than 8 TiB of memory will hit this
limitation and would fail with the following assertion in isa-debugcon:

ASSERT_EFI_ERROR (Status = Already started)
ASSERT /builddir/build/BUILD/edk2-ca407c7246bf/OvmfPkg/SmbiosPlatformDxe/SmbiosPlatformDxe.c(125): !EFI_ERROR (Status)

This change adds an additional offset between tables 17 and 19 handle numbers
when configuring VMs larger than 8 TiB of memory. The value of the offset is
calculated to be equal to the additional space required to be reserved
in order to accomodate more DIMM entries without the table handles colliding.
In normal cases where the VM memory is smaller or equal to 8 TiB, this offset
value is 0. Hence in this case, no additional handle numbers are reserved and
table handle values remain as before.

Since smbios memory is not transmitted over the wire during migration,
this change can break migration for large memory vms if the guest is in the
middle of generating the tables during migration. However, in those
situations, qemu generates invalid table handles anyway with or without this
fix. Hence, we do not preserve the old bug by introducing compat knobs/machine
types.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2023977

Signed-off-by: Ani Sinha <[e-mail]>
Reviewed-by: Igor Mammedov <[e-mail]>
---
 hw/smbios/smbios.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

Patch

diff --git a/hw/smbios/smbios.c b/hw/smbios/smbios.c
index 56b412ce35..44c53797a4 100644
--- a/hw/smbios/smbios.c
+++ b/hw/smbios/smbios.c
@@ -799,12 +799,13 @@  static void smbios_build_type_17_table(unsigned instance, uint64_t size)
     SMBIOS_BUILD_TABLE_POST;
 }
 
-static void smbios_build_type_19_table(unsigned instance,
+static void smbios_build_type_19_table(unsigned instance, unsigned offset,
                                        uint64_t start, uint64_t size)
 {
     uint64_t end, start_kb, end_kb;
 
-    SMBIOS_BUILD_TABLE_PRE(19, T19_BASE + instance, true); /* required */
+    SMBIOS_BUILD_TABLE_PRE(19, T19_BASE + offset + instance,
+                           true); /* required */
 
     end = start + size - 1;
     assert(end > start);
@@ -996,7 +997,7 @@  void smbios_get_tables(MachineState *ms,
                        uint8_t **anchor, size_t *anchor_len,
                        Error **errp)
 {
-    unsigned i, dimm_cnt;
+    unsigned i, dimm_cnt, offset;
 
     if (smbios_legacy) {
         *tables = *anchor = NULL;
@@ -1026,6 +1027,16 @@  void smbios_get_tables(MachineState *ms,
 
         dimm_cnt = QEMU_ALIGN_UP(current_machine->ram_size, MAX_DIMM_SZ) / MAX_DIMM_SZ;
 
+        /*
+         * The offset determines if we need to keep additional space betweeen
+         * table 17 and table 19 header handle numbers so that they do
+         * not overlap. For example, for a VM with larger than 8 TB guest
+         * memory and DIMM like chunks of 16 GiB, the default space between
+         * the two tables (T19_BASE - T17_BASE = 512) is not enough.
+         */
+        offset = (dimm_cnt > (T19_BASE - T17_BASE)) ? \
+                 dimm_cnt - (T19_BASE - T17_BASE) : 0;
+
         smbios_build_type_16_table(dimm_cnt);
 
         for (i = 0; i < dimm_cnt; i++) {
@@ -1033,7 +1044,7 @@  void smbios_get_tables(MachineState *ms,
         }
 
         for (i = 0; i < mem_array_size; i++) {
-            smbios_build_type_19_table(i, mem_array[i].address,
+            smbios_build_type_19_table(i, offset, mem_array[i].address,
                                        mem_array[i].length);
         }