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<fix>[kvm]: limit hot-plug volume to 20 to prevent PCI slot exhaustion (ZSTAC-76384) #3625

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<fix>[kvm]: limit hot-plug volume to 20 to prevent PCI slot exhaustion (ZSTAC-76384) #3625

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4 changes: 4 additions & 0 deletions header/src/main/java/org/zstack/header/volume/MaxDataVolumeNumberExtensionPoint.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6,4 +6,8 @@ public interface MaxDataVolumeNumberExtensionPoint {
String getHypervisorTypeForMaxDataVolumeNumberExtension();

int getMaxDataVolumeNumber();

default int getMaxDataVolumeNumberForRunningVm() {
return getMaxDataVolumeNumber();
}
}
5 changes: 5 additions & 0 deletions plugin/kvm/src/main/java/org/zstack/kvm/KVMConstant.java
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Expand Up @@ -160,6 +160,11 @@ public interface KVMConstant {

Integer DEFAULT_MAX_NIC_QUEUE_NUMBER = 12;

// Maximum data volumes for hot-plug (running VM) due to PCI bus slot constraints.
// i440fx provides 32 PCI slots; ~12 are reserved by system devices and libvirt PCI bridge,
// leaving ~20 slots for hot-plugged virtio-blk data volumes (SharedBlock storage scenario).
int KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG = 20;

Comment on lines +163 to +167
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@coderabbitai coderabbitai bot Mar 27, 2026

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⚠️ Potential issue | 🟠 Major

KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG 可能有一位偏差，无法拦截第 20 块热插场景

当前上限设为 20，而 VolumeBase.vmAttachVolumeValidator 的判断是 vmDataVolumeUsage + 1 > maxDataVolumeNum。这会放行第 20 次挂载请求，和“第 20 次触发 libvirt PCI 槽位不足”的问题描述不一致，可能导致修复不生效。建议将上限调整为 19（或同步调整判断语义）。

🛠 建议修复 
-    // leaving ~20 slots for hot-plugged virtio-blk data volumes (SharedBlock storage scenario).
-    int KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG = 20;
+    // leaving ~19 slots for hot-plugged virtio-blk data volumes (SharedBlock storage scenario).
+    int KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG = 19;
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
// Maximum data volumes for hot-plug (running VM) due to PCI bus slot constraints.
// i440fx provides 32 PCI slots; ~12 are reserved by system devices and libvirt PCI bridge,
// leaving ~20 slots for hot-plugged virtio-blk data volumes (SharedBlock storage scenario).
int KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG = 20;
// Maximum data volumes for hot-plug (running VM) due to PCI bus slot constraints.
// i440fx provides 32 PCI slots; ~12 are reserved by system devices and libvirt PCI bridge,
// leaving ~19 slots for hot-plugged virtio-blk data volumes (SharedBlock storage scenario).
int KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG = 19;
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@plugin/kvm/src/main/java/org/zstack/kvm/KVMConstant.java` around lines 163 -
167, The constant KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG is off by one versus the
validator logic in VolumeBase.vmAttachVolumeValidator (which uses the check
vmDataVolumeUsage + 1 > maxDataVolumeNum), so adjust the limit to prevent
allowing the 20th hot-plug: change KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG from 20
to 19 (or alternatively change the validator's comparison semantics), ensure
references to KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG remain consistent, and run
relevant unit/integration tests around vmAttachVolumeValidator and hot-plug
flows to confirm the 20th attach is rejected.

String CONNECT_HOST_PRIMARYSTORAGE_ERROR = "psError";

String VIRTUALIZER_QEMU_KVM = "qemu-kvm";
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5 changes: 5 additions & 0 deletions plugin/kvm/src/main/java/org/zstack/kvm/KVMHostFactory.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1098,6 +1098,11 @@ public int getMaxDataVolumeNumber() {
return maxDataVolumeNum;
}

@Override
public int getMaxDataVolumeNumberForRunningVm() {
return Math.min(maxDataVolumeNum, KVMConstant.KVM_MAX_DATA_VOLUME_NUMBER_HOT_PLUG);
}

@Override
@AsyncThread
public void managementNodeReady() {
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5 changes: 4 additions & 1 deletion storage/src/main/java/org/zstack/storage/volume/VolumeBase.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3272,7 +3272,10 @@ static void vmAttachVolumeValidator(VmInstanceInventory vmInv, String volumeUuid

PluginRegistry pluginRgty = Platform.getComponentLoader().getComponent(PluginRegistry.class);
MaxDataVolumeNumberExtensionPoint ext = pluginRgty.getExtensionFromMap(hypervisorType, MaxDataVolumeNumberExtensionPoint.class);
int maxDataVolumeNum = ext == null ? VolumeConstant.DEFAULT_MAX_DATA_VOLUME_NUMBER : ext.getMaxDataVolumeNumber();
boolean isRunning = VmInstanceState.Running.toString().equals(vmInv.getState())
|| VmInstanceState.Paused.toString().equals(vmInv.getState());
int maxDataVolumeNum = ext == null ? VolumeConstant.DEFAULT_MAX_DATA_VOLUME_NUMBER
: (isRunning ? ext.getMaxDataVolumeNumberForRunningVm() : ext.getMaxDataVolumeNumber());

long vmDataVolumeUsage = Q.New(VolumeVO.class)
.eq(VolumeVO_.type, VolumeType.Data)
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