linux-kernel - Re: [PATCHv2] x86/mm: Fix memory encryption features advertisement

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Date: Thu, 11 Jan 2024 06:19:46 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>
Cc: x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Tom Lendacky <thomas.lendacky@....com>, linux-coco@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
 Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
Subject: Re: [PATCHv2] x86/mm: Fix memory encryption features advertisement



On 1/11/2024 3:12 AM, Kirill A. Shutemov wrote:
> When memory encryption is enabled, the kernel prints the encryption
> flavor that the system supports.
> 
> The check assumes that everything is AMD SME/SEV if it doesn't have
> the TDX CPU feature set.
> 
> Hyper-V vTOM sets cc_vendor to CC_VENDOR_INTEL when it runs as L2 guest
> on top of TDX, but not X86_FEATURE_TDX_GUEST. Hyper-V only needs memory
> encryption enabled for I/O without the rest of CoCo enabling.
> 
> To avoid confusion, check the cc_vendor directly.
> 
> Possible alternative is to completely removing the print statement.
> For a regular TDX guest, the kernel already prints a message indicating
> that it is booting on TDX. Similarly, AMD and Hyper-V can also display
> a message during their enumeration process.

With this change, will it print "Intel TDX" for Hyper-V?

IMO, since there is already a debug message for type identification, we
can remove this part. 

> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Dexuan Cui <decui@...rosoft.com>
> Cc: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
> ---
>  arch/x86/mm/mem_encrypt.c | 56 +++++++++++++++++++++------------------
>  1 file changed, 30 insertions(+), 26 deletions(-)
> 
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index c290c55b632b..d035bce3a2b0 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -42,38 +42,42 @@ bool force_dma_unencrypted(struct device *dev)
>  
>  static void print_mem_encrypt_feature_info(void)
>  {
> -	pr_info("Memory Encryption Features active:");
> +	pr_info("Memory Encryption Features active: ");
>  
> -	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
> -		pr_cont(" Intel TDX\n");
> -		return;
> -	}
> +	switch (cc_vendor) {
> +	case CC_VENDOR_INTEL:
> +		pr_cont("Intel TDX\n");
> +		break;
> +	case CC_VENDOR_AMD:
> +		pr_cont("AMD");
>  
> -	pr_cont(" AMD");
> -
> -	/* Secure Memory Encryption */
> -	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) {
> +		/* Secure Memory Encryption */
> +		if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) {
>  		/*
>  		 * SME is mutually exclusive with any of the SEV
>  		 * features below.
> -		 */
> -		pr_cont(" SME\n");
> -		return;
> +		*/
> +			pr_cont(" SME\n");
> +			return;
> +		}
> +
> +		/* Secure Encrypted Virtualization */
> +		if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> +			pr_cont(" SEV");
> +
> +		/* Encrypted Register State */
> +		if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
> +			pr_cont(" SEV-ES");
> +
> +		/* Secure Nested Paging */
> +		if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> +			pr_cont(" SEV-SNP");
> +
> +		pr_cont("\n");
> +		break;
> +	default:
> +		pr_cont("Unknown\n");
>  	}
> -
> -	/* Secure Encrypted Virtualization */
> -	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> -		pr_cont(" SEV");
> -
> -	/* Encrypted Register State */
> -	if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
> -		pr_cont(" SEV-ES");
> -
> -	/* Secure Nested Paging */
> -	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> -		pr_cont(" SEV-SNP");
> -
> -	pr_cont("\n");
>  }
>  
>  /* Architecture __weak replacement functions */

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer