linux-kernel - Re: [PATCH v4 7/7] crypto: ccp: Move SEV/SNP Platform initialization to KVM

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Message-ID: <491714b8-6cb7-ac0f-862c-7fdec3be5175@amd.com>
Date: Thu, 20 Feb 2025 15:05:53 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kalra, Ashish" <ashish.kalra@....com>, 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
Cc: michael.roth@....com, dionnaglaze@...gle.com, nikunj@....com,
 ardb@...nel.org, kevinloughlin@...gle.com, Neeraj.Upadhyay@....com,
 aik@....com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-crypto@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: Re: [PATCH v4 7/7] crypto: ccp: Move SEV/SNP Platform initialization
 to KVM

On 2/20/25 14:23, Kalra, Ashish wrote:
> Hello Tom,
> 
> On 2/20/2025 2:03 PM, Tom Lendacky wrote:
>> On 2/19/25 14:55, Ashish Kalra wrote:
>>> From: Ashish Kalra <ashish.kalra@....com>
>>>
>>> SNP initialization is forced during PSP driver probe purely because SNP
>>> can't be initialized if VMs are running.  But the only in-tree user of
>>> SEV/SNP functionality is KVM, and KVM depends on PSP driver for the same.
>>> Forcing SEV/SNP initialization because a hypervisor could be running
>>> legacy non-confidential VMs make no sense.
>>>
>>> This patch removes SEV/SNP initialization from the PSP driver probe
>>> time and moves the requirement to initialize SEV/SNP functionality
>>> to KVM if it wants to use SEV/SNP.
>>>
>>> Suggested-by: Sean Christopherson <seanjc@...gle.com>
>>> Reviewed-by: Alexey Kardashevskiy <aik@....com>
>>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>>> ---
>>>  drivers/crypto/ccp/sev-dev.c | 25 +------------------------
>>>  1 file changed, 1 insertion(+), 24 deletions(-)
>>>
>>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>>> index f0f3e6d29200..99a663dbc2b6 100644
>>> --- a/drivers/crypto/ccp/sev-dev.c
>>> +++ b/drivers/crypto/ccp/sev-dev.c
>>> @@ -1346,18 +1346,13 @@ static int _sev_platform_init_locked(struct sev_platform_init_args *args)
>>>  	if (sev->state == SEV_STATE_INIT)
>>>  		return 0;
>>>  
>>> -	/*
>>> -	 * Legacy guests cannot be running while SNP_INIT(_EX) is executing,
>>> -	 * so perform SEV-SNP initialization at probe time.
>>> -	 */
>>>  	rc = __sev_snp_init_locked(&args->error);
>>>  	if (rc && rc != -ENODEV) {
>>>  		/*
>>>  		 * Don't abort the probe if SNP INIT failed,
>>>  		 * continue to initialize the legacy SEV firmware.
>>>  		 */
>>> -		dev_err(sev->dev, "SEV-SNP: failed to INIT rc %d, error %#x\n",
>>> -			rc, args->error);
>>> +		dev_err(sev->dev, "SEV-SNP: failed to INIT, continue SEV INIT\n");
>>
>> Please don't remove the error information.
>>
> 
> The error(s) are already being printed in __sev_snp_init_locked() otherwise the same
> error will be printed twice, hence removing it here.

Sounds like this change should be in patch #1 then.

Thanks,
Tom

> 
>>>  	}
>>>  
>>>  	/* Defer legacy SEV/SEV-ES support if allowed by caller/module. */
>>> @@ -2505,9 +2500,7 @@ EXPORT_SYMBOL_GPL(sev_issue_cmd_external_user);
>>>  void sev_pci_init(void)
>>>  {
>>>  	struct sev_device *sev = psp_master->sev_data;
>>> -	struct sev_platform_init_args args = {0};
>>>  	u8 api_major, api_minor, build;
>>> -	int rc;
>>>  
>>>  	if (!sev)
>>>  		return;
>>> @@ -2530,16 +2523,6 @@ void sev_pci_init(void)
>>>  			 api_major, api_minor, build,
>>>  			 sev->api_major, sev->api_minor, sev->build);
>>>  
>>> -	/* Initialize the platform */
>>> -	args.probe = true;
>>> -	rc = sev_platform_init(&args);
>>> -	if (rc)
>>> -		dev_err(sev->dev, "SEV: failed to INIT error %#x, rc %d\n",
>>> -			args.error, rc);
>>> -
>>> -	dev_info(sev->dev, "SEV%s API:%d.%d build:%d\n", sev->snp_initialized ?
>>> -		"-SNP" : "", sev->api_major, sev->api_minor, sev->build);
>>> -
>>>  	return;
>>>  
>>>  err:
>>> @@ -2550,10 +2533,4 @@ void sev_pci_init(void)
>>>  
>>>  void sev_pci_exit(void)
>>>  {
>>> -	struct sev_device *sev = psp_master->sev_data;
>>> -
>>> -	if (!sev)
>>> -		return;
>>> -
>>> -	sev_firmware_shutdown(sev);
>>
>> Should this remain? If there's a bug in KVM that somehow skips the
>> shutdown call, then SEV will remain initialized. I think the path is
>> safe to call a second time.
> 
> Ok.
> 
> Thanks,
> Ashish
>