Re: [PATCH] db: add Hyper-V leaf 0x40000001

Hi Tanish,

On Tue, Jul 21, 2026 at 11:01:59PM +0530, Tanish Desai wrote:
>This patch adds CPUID.40000001:EAX, the vendor-neutral Hyper-V
>interface signature ("Hv#1"). It is used by COCONUT SVSM for
>Hyper-V host detection before enabling Hyper-V specific paths.
>
>Signed-off-by: Tanish Desai <[email protected]>
>Link: https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/feature-discovery
>---
> db/xml/leaf_40000001.xml | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
> create mode 100644 db/xml/leaf_40000001.xml
>
>diff --git a/db/xml/leaf_40000001.xml b/db/xml/leaf_40000001.xml
>new file mode 100644
>index 0000000..c37bb90
>--- /dev/null
>+++ b/db/xml/leaf_40000001.xml
>@@ -0,0 +1,29 @@
>+<!--
>+*** SPDX-FileCopyrightText: 2026 Linutronix GmbH
>+*** SPDX-License-Identifier: GPL-2.0-only
>+-->
>+<leaf id="0x40000001">
>+  <desc>Hypervisor interface signature</desc>
>+  <text>
>+    Vendor-neutral hypervisor interface identification.  This determines the
>+    semantics of leaves 0x40000002 through 0x400000ff.  Software should base
>+    compatibility decisions on this signature rather than the vendor ID from
>+    leaf 0x40000000.
>+  </text>
>+  <hypervisors>
>+    <hypervisor>Hyperv</hypervisor>
>+  </hypervisors>

looking at the leaf_40000001 `hypervisors` are put in the subleaf section. Not an
expert, I just noted this. I'll leave to maintainers to decide if it
makes sense to change this or not.

>+  <subleaf id="0">
>+    <eax>
>+      <bit0  len="32" id="hyp_interface"           desc="Hypervisor interface signature">
>+        <text>
>+          Hypervisors conforming to the Microsoft hypervisor interface return
>+          the ASCII signature "Hv#1" (0x31237648) in this field.
>+        </text>
>+        <values>
>+          <value      id="0x31237648"              desc="Hv#1" />
>+        </values>
>+      </bit0>
>+    </eax>
>+  </subleaf>
>+</leaf>
>-- 
>2.15.0
>

Thanks for the patch, this would be very useful for SVSM!

Luigi