x86/kvm: Fix SEV check in sev_map_percpu_data()

JIRA: https://issues.redhat.com/browse/RHEL-84184

This patch is a backport of the following upstream commit:
commit a9ef277
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date:   Wed Jan 24 15:03:17 2024 +0200

    x86/kvm: Fix SEV check in sev_map_percpu_data()

    The function sev_map_percpu_data() checks if it is running on an SEV
    platform by checking the CC_ATTR_GUEST_MEM_ENCRYPT attribute. However,
    this attribute is also defined for TDX.

    To avoid false positives, add a cc_vendor check.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Fixes: 4d96f91 ("x86/sev: Replace occurrences of sev_active() with cc_platform_has()")
    Suggested-by: Borislav Petkov (AMD) <bp@alien8.de>
    Acked-by: David Rientjes <rientjes@google.com>
    Message-Id: <20240124130317.495519-1-kirill.shutemov@linux.intel.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Rafael Aquini <raquini@redhat.com>

Author: Rafael Aquini

arch/x86/kernel/kvm.c

@@ -435,7 +435,8 @@ static void __init sev_map_percpu_data(void)
 {
 	int cpu;
 
-	if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+	if (cc_vendor != CC_VENDOR_AMD ||
+	    !cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
 		return;
 
 	for_each_possible_cpu(cpu) {