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

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Message-ID: <ca14057d-ebdb-4e2d-97b8-5289bada7fe8@linux.microsoft.com>
Date: Thu, 11 Jan 2024 16:14:45 +0100
From: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 "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>
Subject: Re: [PATCHv2] x86/mm: Fix memory encryption features advertisement

On 11/01/2024 15:19, Kuppuswamy Sathyanarayanan wrote:
> 
> 
> 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?

Yes, I just tested on AMD and Intel and the print is accurate now. Thanks.

Reviewed-by: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>

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

If that's the only way to get a fix merged then so be it, but I appreciate having
the possibility of greping for a single prefix for either vendor that the current
code provides.

>>
>> 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 */
>