Merge pull request #9088 from cwhitley-MSFT/IRQL-NOT-LESS-OR-EQUAL

AB#6221: Add troubleshooting guide for IRQL_NOT_LESS_OR_EQUAL bugcheck on Azur…

Author: AmandaAZ

support/azure/virtual-machines/windows/interrupt-request-line-not-less-equal.md

@@ -0,0 +1,43 @@
+---
+title: Bug Check 0x0000001A - IRQL_NOT_LESS_OR_EQUAL
+description: Provides solutions to an issue where an Azure virtual machine (VM) experiences the IRQL_NOT_LESS_OR_EQUAL bug check (0x0000001A).
+ms.date: 06/13/2025
+ms.reviewer: cwhitley, v-weizhu
+ms.service: azure-virtual-machines
+ms.collection: windows
+ms.custom: sap:My VM is not booting
+---
+
+# VM startup is stuck on bug check 0x0000001A - IRQL_NOT_LESS_OR_EQUAL
+
+**Applies to:** :heavy_check_mark: Windows VMs
+
+This article helps you resolve an issue where a Microsoft Azure virtual machine (VM) experiences the **IRQL_NOT_LESS_OR_EQUAL** bug check with the stop code 0x0000001A.
+
+## Symptoms
+
+When you use [Boot diagnostics](./boot-diagnostics.md) to view the screenshot of a VM, the Windows operating system (OS) displays the **IRQL_NOT_LESS_OR_EQUAL** bug check (0x0000001A).
+
+:::image type="content" source="media/interrupt-request-line-not-less-equal/interrupt-request-line-not-less-equal-bug-check-screen.png" alt-text="Screenshot of Windows operating system bug check IRQL_NOT_LESS_OR_EQUAL (0x0000001A).":::
+
+## Cause
+
+This bug check indicates that Windows or a kernel-mode driver tries to access paged memory at an invalid address while operating at a raised interrupt request level (IRQL).
+
+This issue often occurs when the OS of a VM doesn't support more than 64 virtual CPUs (vCPUs), but the VM is configured with a higher vCPU count. For instance, Windows Server 2012 R2 supports a maximum of 64 vCPUs. If a VM running such an OS is provisioned with more than 64 vCPUs, the VM might fail to start and trigger the IRQL_NOT_LESS_OR_EQUAL bug check.
+
+## Resolution
+
+To resolve this issue, use one of the following methods:
+
+- Reduce the number of vCPUs assigned to the VM to 64 or fewer.
+- Rebuild the VM using an OS that supports more than 64 vCPUs, such as Windows Server 2016 or later.
+
+If your VM is already running a supported OS version or is configured with 64 or fewer vCPUs, further investigation is required to determine the specific cause of this issue.
+
+## Collect a memory dump for troubleshooting
+
+To assist with further diagnosis, [collect an OS memory dump file](./collect-os-memory-dump-file.md) and then [create a support request](https://ms.portal.azure.com/#blade/Microsoft_Azure_Support/HelpAndSupportBlade/overview?DMC=troubleshoot) so that Azure support can investigate and help resolve the issue.
+
+
+[!INCLUDE [Azure Help Support](../../../includes/azure-help-support.md)]

support/azure/virtual-machines/windows/media/interrupt-request-line-not-less-equal/interrupt-request-line-not-less-equal-bug-check-screen.png

@@ -336,6 +336,8 @@
       href: applying-group-policy-shortcuts-policy.md
     - name: Azure VM startup hangs at "Applying Software Installation policy"
       href: applying-software-installation-policy.md
+    - name: Azure VM startup hangs at "IRQL_NOT_LESS_OR_EQUAL"
+      href: interrupt-request-line-not-less-equal.md
     - name: Troubleshoot Windows VM OS with missing boot manager
       href: os-bootmgr-missing.md
     - name: OS isn't found