[Qemu-devel] [PATCH] x86/acpi: build SRAT when memory hotplug is enabled

[Thadeu Lima de Souza Cascardo <cascardo@canonical.com>]

Linux uses SRAT to determine the maximum memory in a system, which is
used to determine whether to use the swiotlb for IOMMU or not for a
device that supports only 32 bits of addresses.

When there is no NUMA configuration, qemu will not build SRAT. And when
memory hotplug is done, some Linux device drivers start failing.

Tested by running with -m 512M,slots=8,maxmem=1G, adding the memory,
putting that online and using the system. Without the patch, swiotlb is
not used and ATA driver fails. With the patch, swiotlb is used, no
driver failure is observed.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
---
 hw/i386/acpi-build.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 98dd424678..fb94249779 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -2645,6 +2645,9 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine)
     GArray *tables_blob = tables->table_data;
     AcpiSlicOem slic_oem = { .id = NULL, .table_id = NULL };
     Object *vmgenid_dev;
+    ram_addr_t hotplugabble_address_space_size =
+        object_property_get_int(OBJECT(pcms), PC_MACHINE_MEMHP_REGION_SIZE,
+                                NULL);
 
     acpi_get_pm_info(&pm);
     acpi_get_misc_info(&misc);
@@ -2708,7 +2711,7 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine)
             build_tpm2(tables_blob, tables->linker);
         }
     }
-    if (pcms->numa_nodes) {
+    if (pcms->numa_nodes || hotplugabble_address_space_size) {
         acpi_add_table(table_offsets, tables_blob);
         build_srat(tables_blob, tables->linker, machine);
         if (have_numa_distance) {
-- 
2.11.0