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

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Message-ID: <20240801205638.6603-3-papaluri@amd.com>
Date: Thu, 1 Aug 2024 15:56:38 -0500
From: Pavan Kumar Paluri <papaluri@....com>
To: <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>
CC: Borislav Petkov <bp@...en8.de>, 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>, Brijesh Singh <brijesh.singh@....com>, "H . Peter
 Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, "Pavan Kumar
 Paluri" <papaluri@....com>
Subject: [PATCH 2/2] x86 KVM:SVM: Provide "nosnp" boot option for sev kernel command line

Provide a "nosnp" kernel command line option to prevent enabling of the
RMP and SEV-SNP features in the host/hypervisor. Not initializing the
RMP removes system overhead associated with RMP checks.

Co-developed-by: Eric Van Tassell <Eric.VanTassell@....com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@....com>
Signed-off-by: Pavan Kumar Paluri <papaluri@....com>
---
 Documentation/arch/x86/x86_64/boot-options.rst | 3 +++
 arch/x86/virt/svm/cmdline.c                    | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/Documentation/arch/x86/x86_64/boot-options.rst b/Documentation/arch/x86/x86_64/boot-options.rst
index 137432d34109..3d4e9a7dccf2 100644
--- a/Documentation/arch/x86/x86_64/boot-options.rst
+++ b/Documentation/arch/x86/x86_64/boot-options.rst
@@ -317,3 +317,6 @@ The available options are:
 
    debug
      Enable debug messages.
+
+   nosnp
+     Do not enable SEV-SNP (applies to host/hypervisor only).
diff --git a/arch/x86/virt/svm/cmdline.c b/arch/x86/virt/svm/cmdline.c
index 507549a9c793..1e71c75f0201 100644
--- a/arch/x86/virt/svm/cmdline.c
+++ b/arch/x86/virt/svm/cmdline.c
@@ -24,6 +24,12 @@ 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;
+		}
+
 		pr_info("SEV command-line option '%s' was not recognized\n", s);
 	}
 
-- 
2.34.1