Re: [PATCH v2 2/6] percpu: Bound decrypted storage for all x86 encrypted guests

[Peter Zijlstra]

On Tue, Sep 29, 2026 at 12:02:51AM -0400, Zack Rusin wrote:
> TDX also needs shared per-CPU buffers. Use X86_MEM_ENCRYPT for their
> definition and placement, and provide page-aligned boundaries so the
> architecture can convert each CPU's whole section before registration.
> 
> Define the boundaries in the SMP template or UP data as appropriate.
> Drop the unused DECLARE_PER_CPU_DECRYPTED() macro.
> 
> Suggested-by: Kiryl Shutsemau <kas@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/aqqGUAX65s4LdJkr@thinkstation
> Signed-off-by: Zack Rusin <zack.rusin@xxxxxxxxxxxx>
> ---
>  include/asm-generic/vmlinux.lds.h | 12 ++++++++----
>  include/linux/percpu-defs.h       |  7 ++-----
>  2 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 64bc2bfdd2ec..145fcdbbe9db 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h

> @@ -1022,11 +1024,13 @@
>   * 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
> +#if defined(CONFIG_X86_MEM_ENCRYPT) && defined(CONFIG_SMP)
>  #define PERCPU_DECRYPTED_SECTION					\
>  	. = ALIGN(PAGE_SIZE);						\
> +	__start_percpu_decrypted = .;					\
>  	*(.data..percpu..decrypted)					\
> -	. = ALIGN(PAGE_SIZE);
> +	. = ALIGN(PAGE_SIZE);						\
> +	__end_percpu_decrypted = .;
>  #else
>  #define PERCPU_DECRYPTED_SECTION
>  #endif

So you're page aligning something that will get different protection and
will thus shatter large pages?

That is somewhat uncool. We like large pages, large pages are good.