[SeaBIOS] [RFC PATCH v2] i386: Add _PXM ACPI method to CPU objects

Vasilis Liaskovitis vasilis.liaskovitis at profitbricks.com
Wed Nov 27 14:02:43 CET 2013

This patch adds a _PXM method to ACPI CPU objects for the pc machine. The _PXM
value is derived from the passed in guest info, same way as CPU SRAT entries.

Currently, CPU SRAT entries are only enabled for cpus that are already present
in the system. The SRAT entries for hotpluggable processors are disabled (flags
bit 0 set to 0 in hw/i385/acpi-build.c:build_srat). Section of ACPI
spec mentions "If the Local APIC ID of a dynamically added processor is not
present in the SRAT, a _PXM object must exist for the processor’s device or one
of its ancestors in the ACPI Namespace." Since SRAT entries are not available
for the hot-pluggable processors, a _PXM method must exist for them. Otherwise,
the CPU is hot-added in the wrong NUMA node (default node 0).

Even if CPU SRAT entries are enabled, _PXM method is what the linux kernel
consults on hot-add time. Section 17.2.1 of ACPI spec mentions " OSPM will
consume the SRAT only at boot time. OSPM should use _PXM for any devices that
are hot-added into the system after boot up." To be more precise if SRAT
information is available to the guest kernel, it is used.  However, parsed SRAT
info is reset and lost after hot-remove operations, see kernel commit c4c60524.
This means that on a hot-unplug / hot-replug scenario, and without a _PXM
method, the kernel may put a CPU on different nodes because SRAT info has been
reset by a previous hot-remove operation.

The above hot-remove/hot-add scenario has been tested on master, plus cpu-del
patches from:
With the curret _PXM patch, hot-added CPUs are always placed into the correct
NUMA node, regardless of kernel behaviour.

   Make method return a DWORD integer
   Tested on qemu master + cpu-del patches

Signed-off-by: Vasilis Liaskovitis <vasilis.liaskovitis at profitbricks.com>
Reviewed-by: Thilo Fromm <t-lo at thilo-fromm.de>

 hw/i386/acpi-build.c  |    5 +++++
 hw/i386/ssdt-proc.dsl |    5 +++++
 2 files changed, 10 insertions(+)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index d089e1e..3c11ddc 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -603,6 +603,7 @@ static inline char acpi_get_hex(uint32_t val)
 #define ACPI_PROC_OFFSET_CPUHEX (*ssdt_proc_name - *ssdt_proc_start + 2)
 #define ACPI_PROC_OFFSET_CPUID1 (*ssdt_proc_name - *ssdt_proc_start + 4)
 #define ACPI_PROC_OFFSET_CPUID2 (*ssdt_proc_id - *ssdt_proc_start)
+#define ACPI_PROC_OFFSET_CPUPXM (*ssdt_proc_pxm - *ssdt_proc_start)
 #define ACPI_PROC_SIZEOF (*ssdt_proc_end - *ssdt_proc_start)
 #define ACPI_PROC_AML (ssdp_proc_aml + *ssdt_proc_start)
@@ -724,6 +725,10 @@ build_ssdt(GArray *table_data, GArray *linker,
             proc[ACPI_PROC_OFFSET_CPUHEX+1] = acpi_get_hex(i);
             proc[ACPI_PROC_OFFSET_CPUID1] = i;
             proc[ACPI_PROC_OFFSET_CPUID2] = i;
+            proc[ACPI_PROC_OFFSET_CPUPXM] = guest_info->node_cpu[i];
+            proc[ACPI_PROC_OFFSET_CPUPXM + 1] = 0;
+            proc[ACPI_PROC_OFFSET_CPUPXM + 2] = 0;
+            proc[ACPI_PROC_OFFSET_CPUPXM + 3] = 0;
         /* build this code:
diff --git a/hw/i386/ssdt-proc.dsl b/hw/i386/ssdt-proc.dsl
index 8229bfd..8d4c5bf 100644
--- a/hw/i386/ssdt-proc.dsl
+++ b/hw/i386/ssdt-proc.dsl
@@ -47,6 +47,8 @@ DefinitionBlock ("ssdt-proc.aml", "SSDT", 0x01, "BXPC", "BXSSDT", 0x1)
  * also updating the C code.
         Name(_HID, "ACPI0007")
+        ACPI_EXTRACT_NAME_DWORD_CONST ssdt_proc_pxm
+        Name(PXM, 0xAAAAAAAA)
         External(CPMA, MethodObj)
         External(CPST, MethodObj)
         External(CPEJ, MethodObj)
@@ -59,5 +61,8 @@ DefinitionBlock ("ssdt-proc.aml", "SSDT", 0x01, "BXPC", "BXSSDT", 0x1)
         Method(_EJ0, 1, NotSerialized) {
             CPEJ(ID, Arg0)
+        Method(_PXM, 0) {
+            Return (PXM)
+        }

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