On Fri, Jan 28, 2022 at 11:18:01AM -0600, Brijesh Singh wrote:

Version 2 of GHCB specification provides Non Automatic Exit (NAE) that can

	      ^				  ^			   ^
	      the			  a			   event type

be used by the SEV-SNP guest to communicate with the PSP without risk from
a malicious hypervisor who wishes to read, alter, drop or replay the
messages sent.

SNP_LAUNCH_UPDATE can insert two special pages into the guest’s memory:
the secrets page and the CPUID page. The PSP firmware populate the contents

"populates"

of the secrets page. The secrets page contains encryption keys used by the
guest to interact with the firmware. Because the secrets page is encrypted
with the guest’s memory encryption key, the hypervisor cannot read the
keys. See SEV-SNP firmware spec for further details on the secrets page
format.

Create a platform device that the SEV-SNP guest driver can bind to get the
platform resources such as encryption key and message id to use to
communicate with the PSP. The SEV-SNP guest driver provides a userspace
interface to get the attestation report, key derivation, extended
attestation report etc.

...

+static int __init init_snp_platform_device(void)

snp_init_platform_device()

+{
+	struct snp_guest_platform_data data;
+	u64 gpa;
+
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return -ENODEV;
+
+	gpa = get_secrets_page();
+	if (!gpa)
+		return -ENODEV;
+
+	data.secrets_gpa = gpa;
+	if (platform_device_add_data(&guest_req_device, &data, sizeof(data)))
+		goto e_fail;
+
+	if (platform_device_register(&guest_req_device))
+		goto e_fail;
+
+	pr_info("SNP guest platform device initialized.\n");
+	return 0;
+
+e_fail:
+	pr_err("Failed to initialize SNP guest device\n");
+	return -ENODEV;

So when someone tries to debug why the platform device doesn't register
properly, this error message is ambiguous and two of the error paths
don't even issue one.

Either issue a different error message before you return each time or
remove it completely and let someone who really needs it, add it.

I'd vote for former...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette