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

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Message-ID: <aab18e65-d311-436e-b291-efe3660a5b92@amd.com>
Date: Fri, 7 Mar 2025 15:39:54 -0600
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, 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 3/7/2025 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()).

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. */
>>