linux-kernel - Re: [PATCH v5 08/14] x86/mm: Add generic guest initialization hook

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Date:   Mon, 30 Oct 2023 10:23:09 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
        thomas.lendacky@....com, x86@...nel.org, kvm@...r.kernel.org
Cc:     bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
        dave.hansen@...ux.intel.com, dionnaglaze@...gle.com,
        pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v5 08/14] x86/mm: Add generic guest initialization hook

On 10/29/23 23:36, Nikunj A Dadhania wrote:
> diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> index a37ebd3b4773..a07985a96ca5 100644
> --- a/arch/x86/kernel/x86_init.c
> +++ b/arch/x86/kernel/x86_init.c
> @@ -136,6 +136,7 @@ static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool
>  static bool enc_tlb_flush_required_noop(bool enc) { return false; }
>  static bool enc_cache_flush_required_noop(void) { return false; }
>  static bool is_private_mmio_noop(u64 addr) {return false; }
> +static void enc_init_noop(void) { }
>  
>  struct x86_platform_ops x86_platform __ro_after_init = {
>  	.calibrate_cpu			= native_calibrate_cpu_early,
> @@ -158,6 +159,7 @@ struct x86_platform_ops x86_platform __ro_after_init = {
>  		.enc_status_change_finish  = enc_status_change_finish_noop,
>  		.enc_tlb_flush_required	   = enc_tlb_flush_required_noop,
>  		.enc_cache_flush_required  = enc_cache_flush_required_noop,
> +		.enc_init		   = enc_init_noop,
>  	},
>  };
>  
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 9f27e14e185f..01abecc9a774 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -84,5 +84,8 @@ void __init mem_encrypt_init(void)
>  	/* Call into SWIOTLB to update the SWIOTLB DMA buffers */
>  	swiotlb_update_mem_attributes();
>  
> +	if (x86_platform.guest.enc_init)
> +		x86_platform.guest.enc_init();
> +
>  	print_mem_encrypt_feature_info();
>  }

How does '.enc_init' ever get set to NULL?  Isn't the point of having
and using a 'noop' function so that you don't have to do NULL checks?