Re: [PATCH 3/3] x86/sev: Add SEV-SNP CipherTextHiding support

[Kalra, Ashish]

Hi Tom,

On 8/15/2024 10:58 AM, Tom Lendacky wrote:
>> +
>>  static bool psp_dead;
>>  static int psp_timeout;
>>  
>> @@ -1053,6 +1069,36 @@ static void snp_set_hsave_pa(void *arg)
>>  	wrmsrl(MSR_VM_HSAVE_PA, 0);
>>  }
>>  
>> +static void sev_snp_enable_ciphertext_hiding(struct sev_data_snp_init_ex *data, int *error)
>> +{
>> +	struct psp_device *psp = psp_master;
>> +	struct sev_device *sev;
>> +	unsigned int edx;
>> +
>> +	sev = psp->sev_data;
>> +
>> +	/*
>> +	 * Check if CipherTextHiding feature is supported and enabled
>> +	 * in the Platform/BIOS.
>> +	 */
>> +	if (sev->feat_info.ecx & FEAT_CIPHERTEXTHIDING_SUPPORTED &&
>> +	    sev->snp_plat_status.ciphertext_hiding_cap) {
> I'm not sure you need both checks. Either the platform status or the
> feature info check should be enough. Can you check on that?
>
FEATURE_INFO only indicates if SEV FW is capable of ciphertext hiding and SNP_PLATFORM_STATUS ciphertext_hiding_cap bit indicates if the CTH feature is enabled in BIOS, so both checks are needed.

Thanks, Ashish