Re: [PATCH v4] x86/mm/64: free the gap between BSS_MAIN and BSS_DECRYPTED

[Dave Hansen]

On 7/20/26 04:20, Hamza Mahfooz wrote:
> This region is unused and takes up, up to 2 MiB
> of memory if AMD_MEM_ENCRYPT is enabled. So, free it in
> mem_encrypt_free_decrypted_mem().

For something like this, I'd really appreciate if contributors bring
_some_ kind of mention of testing to the changelog.

A great addition to this would be a blurb that mentioned an increase in
MemFree on boot, or a note about the delta in dmesg on startup that
shows the patch working.

> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 4711a35e706c..179578a08da1 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -88,6 +88,8 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
>   * decrypted to avoid exposing more than we wish.
>   */
>  #define BSS_DECRYPTED						\
> +	. = ALIGN(PAGE_SIZE);					\
> +	__start_bss_decrypted_gap = .;				\
>  	. = ALIGN(PMD_SIZE);					\
>  	__start_bss_decrypted = .;				\
>  	__pi___start_bss_decrypted = .;				\
> diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
> index 2f8c32173972..8d518571ae5c 100644
> --- a/arch/x86/mm/mem_encrypt_amd.c
> +++ b/arch/x86/mm/mem_encrypt_amd.c
> @@ -566,4 +566,10 @@ void __init mem_encrypt_free_decrypted_mem(void)
>  	}
>  
>  	free_init_pages("unused decrypted", vaddr, vaddr_end);
> +
> +	vaddr = PFN_ALIGN(__start_bss_decrypted_gap);
> +	vaddr_end = PFN_ALIGN(__start_bss_decrypted);
> +
> +	free_kernel_image_pages("unused kernel image (bss_decrypted gap)",
> +				(void *)vaddr, (void *)vaddr_end);
>  }

What purpose do the two new PFN_ALIGN()s serve?