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

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Message-ID: <85d4d61e-b56b-4e8e-ba3d-f239b648f47c@amd.com>
Date: Thu, 15 Aug 2024 15:30:58 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Tom Lendacky <thomas.lendacky@....com>, seanjc@...gle.com,
 pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, herbert@...dor.apana.org.au
Cc: x86@...nel.org, john.allen@....com, davem@...emloft.net,
 michael.roth@....com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-crypto@...r.kernel.org
Subject: Re: [PATCH 3/3] x86/sev: Add SEV-SNP CipherTextHiding support

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