tpm-tis device for ARM virt

[Jim Fehlig]

Hi All,

I received a private bug report that starting a VM with swtpm device fails with 
qemu-system-aarch64. The VM config has

     <tpm model='tpm-tis'>
       <backend type='emulator' version='2.0'/>
      </tpm>

QEMU reports the following error

error: internal error: process exited while connecting to monitor: 
2021-02-07T05:15:35.378927Z qemu-system-aarch64: -device 
tpm-tis,tpmdev=tpm-tpm0,id=tpm0: 'tpm-tis' is not a valid device model name

Indeed it appears the device name is 'tpm-tis-device' [1][2] for ARM virt. The 
similar yet different device naming between x86 and ARM is unfortunate. IIUC, 
the devices are the same between the architectures, i.e. they both emulate a TPM 
device conforming to the TIS spec. If so, adding a 'tpm-tis-device' to 
virDomainTPMModel seems redundant. I assume the naming difference should be 
handled internally, e.g. something like the below patch to qemuBuildTPMDevStr? I 
can send a proper patch if this is an acceptable approach.

Regards,
Jim

[1] https://qemu.readthedocs.io/en/latest/specs/tpm.html
[2] https://github.com/qemu/qemu/commit/c294ac327ca99342b90bd3a83d2cef9b447afaa7

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 92036d26c0..5154611ccd 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -9198,6 +9198,9 @@ qemuBuildTPMDevStr(const virDomainDef *def,
      g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER;
      const char *model = virDomainTPMModelTypeToString(tpm->model);

+    if (tpm->model == VIR_DOMAIN_TPM_MODEL_TIS && def->os.arch == VIR_ARCH_AARCH64)
+        model = "tpm-tis-device";
+
      virBufferAsprintf(&buf, "%s,tpmdev=tpm-%s,id=%s",
                        model, tpm->info.alias, tpm->info.alias);