x86/mm: Handle decryption/re-encryption of bss_decrypted consistently

sme_postprocess_startup() decrypts the bss_decrypted section when
sme_me_mask is non-zero.

mem_encrypt_free_decrypted_mem() re-encrypts the unused portion based
on CC_ATTR_MEM_ENCRYPT.

In a Hyper-V guest VM using vTOM, these conditions are not equivalent
as sme_me_mask is always zero when using vTOM. Consequently,
mem_encrypt_free_decrypted_mem() attempts to re-encrypt memory that was
never decrypted.

So check sme_me_mask in mem_encrypt_free_decrypted_mem() too.

Hyper-V guests using vTOM don't need the bss_decrypted section to be
decrypted, so skipping the decryption/re-encryption doesn't cause a
problem.
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/1678329614-3482-5-git-send-email-mikelley@microsoft.com

arch/x86/mm/mem_encrypt_amd.c

@@ -513,10 +513,14 @@ void __init mem_encrypt_free_decrypted_mem(void)
 	npages = (vaddr_end - vaddr) >> PAGE_SHIFT;
 
 	/*
-	 * The unused memory range was mapped decrypted, change the encryption
-	 * attribute from decrypted to encrypted before freeing it.
+	 * If the unused memory range was mapped decrypted, change the encryption
+	 * attribute from decrypted to encrypted before freeing it. Base the
+	 * re-encryption on the same condition used for the decryption in
+	 * sme_postprocess_startup(). Higher level abstractions, such as
+	 * CC_ATTR_MEM_ENCRYPT, aren't necessarily equivalent in a Hyper-V VM
+	 * using vTOM, where sme_me_mask is always zero.
 	 */
-	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
+	if (sme_me_mask) {
 		r = set_memory_encrypted(vaddr, npages);
 		if (r) {
 			pr_warn("failed to free unused decrypted pages\n");