linux-kernel - Re: [PATCH v8 1/2] x86/mm: add .bss..decrypted section to hold shared variables

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Date:   Fri, 14 Sep 2018 01:24:53 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Brijesh Singh <brijesh.singh@....com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v8 1/2] x86/mm: add .bss..decrypted section to hold shared
 variables

On Thu, 13 Sep 2018, Brijesh Singh wrote:
>  
> +void __weak mem_encrypt_free_decrypted_mem(void) { }
> +
>  void __ref free_initmem(void)
>  {
>  	e820__reallocate_tables();
>  
> +	mem_encrypt_free_decrypted_mem();
> +
>  	free_kernel_image_pages(&__init_begin, &__init_end);
>  }
>  
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index b2de398..718acdf 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -348,6 +348,16 @@ bool sev_active(void)
>  EXPORT_SYMBOL(sev_active);
>  
>  /* Architecture __weak replacement functions */
> +void __init mem_encrypt_free_decrypted_mem(void)
> +{
> +	if (mem_encrypt_active())
> +		return;

Why?

> +
> +	free_init_pages("unused decrypted",
> +			(unsigned long)__start_bss_decrypted_unused,
> +			(unsigned long)__end_bss_decrypted);

Everything _AFTER_ __start_bss_decrypted_unused _IS_ unused and can be
freed. No conditional nothing. It's unused in any case.

Thanks,

	tglx