[Patch v4 04/13] x86/mm: Handle decryption/re-encryption of bss_decrypted consistently

[Michael Kelley]

Current code in sme_postprocess_startup() decrypts the bss_decrypted
section when sme_me_mask is non-zero.  But code in
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.

Fix this in mem_encrypt_free_decrypted_mem() by conditioning the
re-encryption on the same test for non-zero sme_me_mask.  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.

Fixes: e9d1d2bb75b2 ("treewide: Replace the use of mem_encrypt_active() with cc_platform_has()")
Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
 arch/x86/mm/mem_encrypt_amd.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
index 9c4d8db..e0b51c0 100644
--- a/arch/x86/mm/mem_encrypt_amd.c
+++ b/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");
-- 
1.8.3.1