Question about SEV* guests and automatic firmware selection

[Jim Fehlig via Devel]

Hi All,

While investigating an internal bug report, we noticed that a minimal firmware 
auto-selection configuration along with SEV* fails to find a match. E.g. the 
following config

<domain type="kvm">
  <os firmware="efi">
    <type arch="x86_64" machine="q35">hvm</type>
    <boot dev="hd"/>
  </os>
  <launchSecurity type="sev">
    <policy>0x07</policy>
  </launchSecurity>
...
</domain>

Fails with "Unable to find 'efi' firmware that is compatible with the current 
configuration". A firmware that should match has the following json description

{
    "description": "UEFI firmware for x86_64, with AMD SEV",
    "interface-types": [
        "uefi"
    ],
    "mapping": {
        "device": "flash",
        "mode": "stateless",
        "executable": {
            "filename": "/usr/share/qemu/ovmf-x86_64-sev.bin",
            "format": "raw"
        }
    },
    "targets": [
        {
            "architecture": "x86_64",
            "machines": [
                "pc-q35-*"
            ]
        }
    ],
    "features": [
        "acpi-s4",
        "amd-sev",
        "amd-sev-es",
        "amd-sev-snp",
        "verbose-dynamic"
    ],
    "tags": [

    ]
}

Auto-selection works fine if I specify a 'stateless' firmware, e.g. amend the 
above config with

  <os firmware="efi">
    <type arch="x86_64" machine="q35">hvm</type>
    <loader stateless="yes"/>
    <boot dev="hd"/>
  </os>

Being unfamiliar with the firmware auto-selection code, I tried the below naive 
hack, which only led to test failures and the subsequent runtime error "unable 
to find any master var store for loader: /usr/share/qemu/ovmf-x86_64-sev.bin". 
Should auto-selection work with the minimal config, or is it expected that user 
also specify a stateless firmware?

Regards,
Jim

diff --git a/src/qemu/qemu_firmware.c b/src/qemu/qemu_firmware.c
index 2d0ec0b4fa..660b74141a 100644
--- a/src/qemu/qemu_firmware.c
+++ b/src/qemu/qemu_firmware.c
@@ -1293,15 +1293,17 @@ qemuFirmwareMatchDomain(const virDomainDef *def,
             return false;
         }

-        if (loader && loader->stateless == VIR_TRISTATE_BOOL_YES) {
-            if (flash->mode != QEMU_FIRMWARE_FLASH_MODE_STATELESS) {
-                VIR_DEBUG("Discarding loader without stateless flash");
-                return false;
-            }
-        } else {
-            if (flash->mode != QEMU_FIRMWARE_FLASH_MODE_SPLIT) {
-                VIR_DEBUG("Discarding loader without split flash");
-                return false;
+        if (loader) {
+            if (loader->stateless == VIR_TRISTATE_BOOL_YES) {
+                if (flash->mode != QEMU_FIRMWARE_FLASH_MODE_STATELESS) {
+                    VIR_DEBUG("Discarding loader without stateless flash");
+                    return false;
+                }
+            } else if (loader->stateless == VIR_TRISTATE_BOOL_NO) {
+                if (flash->mode != QEMU_FIRMWARE_FLASH_MODE_SPLIT) {
+                    VIR_DEBUG("Discarding loader without split flash");
+                    return false;
+                }
             }
         }