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

[Kiryl Shutsemau <kas@kernel.org>]

On Wed, Sep 16, 2026 at 01:05:39AM -0400, Zack Rusin wrote:
> 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@broadcom.com>
> ---
>  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")

DECLARE_PER_CPU_DECRYPTED() is not used anywhere. Do we want to drop it?

Otherwise:

Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov