[PATCH v1 1/2] percpu: Use X86_MEM_ENCRYPT for decrypted per-CPU data

[Zack Rusin]

Decrypted per-CPU data is gated by AMD_MEM_ENCRYPT. With
INTEL_TDX_GUEST=y and AMD_MEM_ENCRYPT=n it falls back to ordinary
per-CPU storage, so converting a variable to shared memory can expose
unrelated data on the same page.

Gate the declarations and linker section on X86_MEM_ENCRYPT, which both
AMD_MEM_ENCRYPT and INTEL_TDX_GUEST select. Existing AMD configurations
are unchanged.

Keep the decrypted subsection page-aligned at both ends. The per-CPU
template and each allocated per-CPU unit are also page-aligned, so page
conversion cannot expose ordinary per-CPU data. TDX-only configurations
may need additional space for this alignment and isolation.

Signed-off-by: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
---
 include/asm-generic/vmlinux.lds.h | 2 +-
 include/linux/percpu-defs.h       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2988aa12f66..1448e791773e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -1013,7 +1013,7 @@
  * Note: We use a separate section so that only this section gets
  * decrypted to avoid exposing more than we wish.
  */
-#ifdef CONFIG_AMD_MEM_ENCRYPT
+#ifdef CONFIG_X86_MEM_ENCRYPT
 #define PERCPU_DECRYPTED_SECTION					\
 	. = ALIGN(PAGE_SIZE);						\
 	*(.data..percpu..decrypted)					\
diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index dbe3267a0a13..54ce1442d918 100644
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -172,7 +172,7 @@
  * Declaration/definition used for per-CPU variables that should be accessed
  * as decrypted when memory encryption is enabled in the guest.
  */
-#ifdef CONFIG_AMD_MEM_ENCRYPT
+#ifdef CONFIG_X86_MEM_ENCRYPT
 #define DECLARE_PER_CPU_DECRYPTED(type, name)				\
 	DECLARE_PER_CPU_SECTION(type, name, "..decrypted")
 
-- 
2.53.0