linux-kernel - Re: [PATCH v6 5/7] crypto: ccp - Add support to enable CipherTextHiding on SNP_INIT

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Message-ID: <96079fb9-756b-a419-335b-3a78331af4f8@amd.com>
Date: Tue, 15 Jul 2025 11:34:41 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, corbet@....net, seanjc@...gle.com,
 pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 john.allen@....com, herbert@...dor.apana.org.au, davem@...emloft.net,
 akpm@...ux-foundation.org, rostedt@...dmis.org, paulmck@...nel.org
Cc: nikunj@....com, Neeraj.Upadhyay@....com, aik@....com, ardb@...nel.org,
 michael.roth@....com, arnd@...db.de, linux-doc@...r.kernel.org,
 linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Subject: Re: [PATCH v6 5/7] crypto: ccp - Add support to enable
 CipherTextHiding on SNP_INIT_EX

On 7/14/25 17:40, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> To enable ciphertext hiding, it must be specified in the SNP_INIT_EX
> command as part of SNP initialization.
> 
> Modify the sev_platform_init_args structure, which is used as input to
> sev_platform_init(), to include a field that, when non-zero,
> indicates that ciphertext hiding should be enabled and specifies the
> maximum ASID that can be used for an SEV-SNP guest.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  drivers/crypto/ccp/sev-dev.c | 12 +++++++++---
>  include/linux/psp-sev.h      | 10 ++++++++--
>  2 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index ed18cd113724..9709c140ab19 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -1186,7 +1186,7 @@ static int snp_filter_reserved_mem_regions(struct resource *rs, void *arg)
>  	return 0;
>  }
>  
> -static int __sev_snp_init_locked(int *error)
> +static int __sev_snp_init_locked(int *error, unsigned int max_snp_asid)
>  {
>  	struct psp_device *psp = psp_master;
>  	struct sev_data_snp_init_ex data;
> @@ -1247,6 +1247,12 @@ static int __sev_snp_init_locked(int *error)
>  		}
>  
>  		memset(&data, 0, sizeof(data));
> +
> +		if (max_snp_asid) {
> +			data.ciphertext_hiding_en = 1;
> +			data.max_snp_asid = max_snp_asid;
> +		}
> +
>  		data.init_rmp = 1;
>  		data.list_paddr_en = 1;
>  		data.list_paddr = __psp_pa(snp_range_list);
> @@ -1433,7 +1439,7 @@ static int _sev_platform_init_locked(struct sev_platform_init_args *args)
>  	if (sev->sev_plat_status.state == SEV_STATE_INIT)
>  		return 0;
>  
> -	rc = __sev_snp_init_locked(&args->error);
> +	rc = __sev_snp_init_locked(&args->error, args->max_snp_asid);
>  	if (rc && rc != -ENODEV)
>  		return rc;
>  
> @@ -1516,7 +1522,7 @@ static int snp_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_req
>  {
>  	int error, rc;
>  
> -	rc = __sev_snp_init_locked(&error);
> +	rc = __sev_snp_init_locked(&error, 0);
>  	if (rc) {
>  		argp->error = SEV_RET_INVALID_PLATFORM_STATE;
>  		return rc;
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index d83185b4268b..e0dbcb4b4fd9 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -748,10 +748,13 @@ struct sev_data_snp_guest_request {
>  struct sev_data_snp_init_ex {
>  	u32 init_rmp:1;
>  	u32 list_paddr_en:1;
> -	u32 rsvd:30;
> +	u32 rapl_dis:1;
> +	u32 ciphertext_hiding_en:1;
> +	u32 rsvd:28;
>  	u32 rsvd1;
>  	u64 list_paddr;
> -	u8  rsvd2[48];
> +	u16 max_snp_asid;
> +	u8  rsvd2[46];
>  } __packed;
>  
>  /**
> @@ -800,10 +803,13 @@ struct sev_data_snp_shutdown_ex {
>   * @probe: True if this is being called as part of CCP module probe, which
>   *  will defer SEV_INIT/SEV_INIT_EX firmware initialization until needed
>   *  unless psp_init_on_probe module param is set
> + * @max_snp_asid: When non-zero, enable ciphertext hiding and specify the
> + *  maximum ASID that can be used for an SEV-SNP guest.
>   */
>  struct sev_platform_init_args {
>  	int error;
>  	bool probe;
> +	unsigned int max_snp_asid;
>  };
>  
>  /**