[RFC PATCH 2/5] OvmfPkg/CpuHotplugSmm: handle fw_remove

["Ankur Arora" <ankur.a.arora@oracle.com>]

Limit collection of APIC IDs for hot-unplug events to CPUs with
fw_remove set. Additionally we now ignore CPUs which have only
remove set.

Protocol documented here:
https://lore.kernel.org/qemu-devel/20201204170939.1815522-3-imammedo@redhat.com/

Also define QEMU_CPUHP_STAT_EJECTED while we are at it.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 OvmfPkg/CpuHotplugSmm/QemuCpuhp.c             | 35 ++++++++++++++-----
 .../Include/IndustryStandard/QemuCpuHotplug.h |  2 ++
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/OvmfPkg/CpuHotplugSmm/QemuCpuhp.c b/OvmfPkg/CpuHotplugSmm/QemuCpuhp.c
index 8d4a6693c8d6..2dd783ebf42e 100644
--- a/OvmfPkg/CpuHotplugSmm/QemuCpuhp.c
+++ b/OvmfPkg/CpuHotplugSmm/QemuCpuhp.c
@@ -205,7 +205,7 @@ QemuCpuhpCollectApicIds (
     UINT8   CpuStatus;
     APIC_ID *ExtendIds;
     UINT32  *ExtendCount;
-    APIC_ID NewApicId;
+    APIC_ID OpApicId;
 
     //
     // Write CurrentSelector (which is valid) to the CPU selector register.
@@ -245,10 +245,10 @@ QemuCpuhpCollectApicIds (
     if ((CpuStatus & QEMU_CPUHP_STAT_INSERT) != 0) {
       //
       // The "insert" event guarantees the "enabled" status; plus it excludes
-      // the "remove" event.
+      // the "fw_remove" event.
       //
       if ((CpuStatus & QEMU_CPUHP_STAT_ENABLED) == 0 ||
-          (CpuStatus & QEMU_CPUHP_STAT_REMOVE) != 0) {
+          (CpuStatus & QEMU_CPUHP_STAT_FW_REMOVE) != 0) {
         DEBUG ((DEBUG_ERROR, "%a: CurrentSelector=%u CpuStatus=0x%x: "
           "inconsistent CPU status\n", __FUNCTION__, CurrentSelector,
           CpuStatus));
@@ -260,12 +260,31 @@ QemuCpuhpCollectApicIds (
 
       ExtendIds   = PluggedApicIds;
       ExtendCount = PluggedCount;
-    } else if ((CpuStatus & QEMU_CPUHP_STAT_REMOVE) != 0) {
-      DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u: remove\n", __FUNCTION__,
+    } else if ((CpuStatus & QEMU_CPUHP_STAT_FW_REMOVE) != 0) {
+      //
+      // "fw_remove" event guarantees "enabled".
+      //
+      if ((CpuStatus & QEMU_CPUHP_STAT_ENABLED) == 0) {
+        DEBUG ((DEBUG_ERROR, "%a: CurrentSelector=%u CpuStatus=0x%x: "
+          "inconsistent CPU status\n", __FUNCTION__, CurrentSelector,
+          CpuStatus));
+        return EFI_PROTOCOL_ERROR;
+      }
+
+      DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u: fw_remove\n", __FUNCTION__,
         CurrentSelector));
 
       ExtendIds   = ToUnplugApicIds;
       ExtendCount = ToUnplugCount;
+    } else if ((CpuStatus & QEMU_CPUHP_STAT_REMOVE) != 0) {
+      //
+      // Let the OSPM deal with the "remove" event.
+      //
+      DEBUG ((DEBUG_INFO, "%a: CurrentSelector=%u: remove (ignored)\n", __FUNCTION__,
+        CurrentSelector));
+
+      CurrentSelector++;
+      continue;
     } else {
       DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u: no event\n",
         __FUNCTION__, CurrentSelector));
@@ -281,10 +300,10 @@ QemuCpuhpCollectApicIds (
       return EFI_BUFFER_TOO_SMALL;
     }
     QemuCpuhpWriteCommand (MmCpuIo, QEMU_CPUHP_CMD_GET_ARCH_ID);
-    NewApicId = QemuCpuhpReadCommandData (MmCpuIo);
+    OpApicId = QemuCpuhpReadCommandData (MmCpuIo);
     DEBUG ((DEBUG_VERBOSE, "%a: ApicId=" FMT_APIC_ID "\n", __FUNCTION__,
-      NewApicId));
-    ExtendIds[(*ExtendCount)++] = NewApicId;
+      OpApicId, ExtendCount));
+    ExtendIds[(*ExtendCount)++] = OpApicId;
 
     //
     // We've processed the CPU with (known) pending events, but we must never
diff --git a/OvmfPkg/Include/IndustryStandard/QemuCpuHotplug.h b/OvmfPkg/Include/IndustryStandard/QemuCpuHotplug.h
index a34a6d3fae61..692e3072598c 100644
--- a/OvmfPkg/Include/IndustryStandard/QemuCpuHotplug.h
+++ b/OvmfPkg/Include/IndustryStandard/QemuCpuHotplug.h
@@ -34,6 +34,8 @@
 #define QEMU_CPUHP_STAT_ENABLED                BIT0
 #define QEMU_CPUHP_STAT_INSERT                 BIT1
 #define QEMU_CPUHP_STAT_REMOVE                 BIT2
+#define QEMU_CPUHP_STAT_EJECTED                BIT3
+#define QEMU_CPUHP_STAT_FW_REMOVE              BIT4
 
 #define QEMU_CPUHP_RW_CMD_DATA               0x8
 
-- 
2.25.4