linux-kernel - Re: [PATCH v6 1/8] crypto: ccp: Abort doing SEV INIT if SNP INIT fails

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Message-ID: <0511e641-a122-6ece-ec83-8340b5d08e39@amd.com>
Date: Fri, 7 Mar 2025 15:43:50 -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 v6 1/8] crypto: ccp: Abort doing SEV INIT if SNP INIT
 fails

On 3/7/25 15:39, Kalra, Ashish wrote:
> On 3/7/2025 3:29 PM, Tom Lendacky wrote:
>> On 3/7/25 15:06, Kalra, Ashish wrote:
>>> On 3/7/2025 2:57 PM, Tom Lendacky wrote:
>>>> On 3/7/25 14:54, Tom Lendacky wrote:
>>>>> On 3/6/25 17:09, Ashish Kalra wrote:
>>>>>> From: Ashish Kalra <ashish.kalra@....com>
>>>>>>
>>>>>> If SNP host support (SYSCFG.SNPEn) is set, then RMP table must be
>>>>>
>>>>> s/RMP/the RMP/
>>>>>
>>>>>> initialized up before calling SEV INIT.
>>>>>
>>>>> s/up//
>>>>>
>>>>>>
>>>>>> In other words, if SNP_INIT(_EX) is not issued or fails then
>>>>>> SEV INIT will fail once SNP host support (SYSCFG.SNPEn) is enabled.
>>>>>
>>>>> s/once/if/
>>>>>
>>>>>>
>>>>>> Fixes: 1ca5614b84eed ("crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP")
>>>>>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>>>>>> ---
>>>>>>  drivers/crypto/ccp/sev-dev.c | 7 ++-----
>>>>>>  1 file changed, 2 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>>>>>> index 2e87ca0e292a..a0e3de94704e 100644
>>>>>> --- a/drivers/crypto/ccp/sev-dev.c
>>>>>> +++ b/drivers/crypto/ccp/sev-dev.c
>>>>>> @@ -1112,7 +1112,7 @@ static int __sev_snp_init_locked(int *error)
>>>>>>  	if (!sev_version_greater_or_equal(SNP_MIN_API_MAJOR, SNP_MIN_API_MINOR)) {
>>>>>>  		dev_dbg(sev->dev, "SEV-SNP support requires firmware version >= %d:%d\n",
>>>>>>  			SNP_MIN_API_MAJOR, SNP_MIN_API_MINOR);
>>>>>> -		return 0;
>>>>>> +		return -EOPNOTSUPP;
>>>>>>  	}
>>>>>>  
>>>>>>  	/* SNP_INIT requires MSR_VM_HSAVE_PA to be cleared on all CPUs. */
>>>>>> @@ -1325,12 +1325,9 @@ static int _sev_platform_init_locked(struct sev_platform_init_args *args)
>>>>>>  	 */
>>>>>>  	rc = __sev_snp_init_locked(&args->error);
>>>>>>  	if (rc && rc != -ENODEV) {
>>>>>
>>>>> Can we get ride of this extra -ENODEV check? It can only be returned
>>>>> because of the same check that is made earlier in this function so it
>>>>> doesn't really serve any purpose from what I can tell.
>>>>>
>>>>> Just make this "if (rc) {"
>>>>
>>>> My bad... -ENODEV is returned if cc_platform_has(CC_ATTR_HOST_SEV_SNP) is
>>>> false, never mind.
>>>
>>> Yes, that's what i was going to reply with ... we want to continue with
>>> SEV INIT if SNP host support is not enabled.
>>
>> Although we could get rid of that awkward if statement by doing...
>>
>> 	if (cc_platform_has(CC_ATTR_HOST_SEV_SNP)) {
>> 		rc = __sev_snp_init_locked(&args->error);
>> 		if (rc) {
>> 			dev_err(sev->dev, ...
>> 			return rc;
>> 		}
>> 	}
>>
>> And deleting the cc_platform_has() check from __sev_snp_init_locked().
> 
> We probably have to keep the cc_platform_has() check in
> __sev_snp_init_locked() for the implicit SNP INIT being issued
> for various SNP specific ioctl's (via snp_move_to_init_state()).

Oh, yeah, the very next patch calls into __sev_snp_init_locked() now.

Thanks,
Tom

> 
> Thanks,
> Ashish
> 
>>>>>
>>>>>> -		/*
>>>>>> -		 * 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);
>>>>>> +		return rc;
>>>>>>  	}
>>>>>>  
>>>>>>  	/* Defer legacy SEV/SEV-ES support if allowed by caller/module. */
>>>
>