virt/coco/sev-guest: Check SEV_SNP attribute at probe time

No need to check it on every ioctl. And yes, this is a common SEV driver
but it does only SNP-specific operations currently. This can be
revisited later, when more use cases appear.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20230307192449.24732-3-bp@alien8.de

arch/x86/kernel/sev.c

@@ -2183,9 +2183,6 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	struct ghcb *ghcb;
 	int ret;
 
-	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
-		return -ENODEV;
-
 	if (!fw_err)
 		return -EINVAL;
 

drivers/virt/coco/sev-guest/sev-guest.c

@@ -703,6 +703,9 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	void __iomem *mapping;
 	int ret;
 
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return -ENODEV;
+
 	if (!dev->platform_data)
 		return -ENODEV;