linux-kernel - Re: [PATCH v7 2/2] x86 KVM:SVM: Provide "nosnp" boot option for sev kernel command line

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Message-ID: <5c3344b9-e896-e93b-6853-1bff83d6544c@amd.com>
Date: Mon, 14 Oct 2024 16:09:45 -0500
From: "Paluri, PavanKumar" <papaluri@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-coco@...ts.linux.dev, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Eric Van Tassell <Eric.VanTassell@....com>,
 Tom Lendacky <thomas.lendacky@....com>, Ashish Kalra <ashish.kalra@....com>,
 Michael Roth <michael.roth@....com>, "H . Peter Anvin" <hpa@...or.com>,
 Peter Zijlstra <peterz@...radead.org>, Dhaval Giani <dhaval.giani@....com>
Subject: Re: [PATCH v7 2/2] x86 KVM:SVM: Provide "nosnp" boot option for sev
 kernel command line

Hello Boris,

On 10/14/2024 10:40 AM, Borislav Petkov wrote:
> On Mon, Oct 14, 2024 at 08:09:48AM -0500, Pavan Kumar Paluri wrote:
>> @@ -25,6 +26,12 @@ static int __init init_sev_config(char *str)
>>  			continue;
>>  		}
>>  
>> +		if (!strcmp(s, "nosnp")) {
>> +			setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
>> +			cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
>> +			continue;
>> +		}
> 
> Well, if it is a HV-only option, then it better be such:
> 
> @@ -25,6 +26,17 @@ static int __init init_sev_config(char *str)
>  			continue;
>  		}
>  
> +		if (!strcmp(s, "nosnp")) {
> +			if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) {

Sure, it does make sense to add this check since nosnp is only a HV option.

Thanks,
Pavan

> +				setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
> +				cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
> +				continue;
> +			} else {
> +				goto warn;
> +			}
> +		}
> +
> +warn:
>  		pr_info("SEV command-line option '%s' was not recognized\n", s);
>  	}
>  
>