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: <20241014154040.GBZw07eBVDJoLJZV0w@fat_crate.local>
Date: Mon, 14 Oct 2024 17:40:40 +0200
From: Borislav Petkov <bp@...en8.de>
To: Pavan Kumar Paluri <papaluri@....com>
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

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)) {
+				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);
 	}
 

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette