linux-kernel - [PATCH v2 2/2] x86 KVM:SVM: Provide "nosnp" boot option for sev kernel command line

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Message-ID: <20240903003511.1530454-3-papaluri@amd.com>
Date: Mon, 2 Sep 2024 19:35:11 -0500
From: Pavan Kumar Paluri <papaluri@....com>
To: <linux-kernel@...r.kernel.org>
CC: <linux-doc@...r.kernel.org>, 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>, "H . Peter Anvin" <hpa@...or.com>,
	"Peter Zijlstra" <peterz@...radead.org>, Pavan Kumar Paluri
	<papaluri@....com>
Subject: [PATCH v2 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>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
---
 Documentation/arch/x86/x86_64/boot-options.rst | 3 +++
 arch/x86/virt/svm/cmdline.c                    | 7 +++++++
 2 files changed, 10 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 4fe34e831d8f..43039ec67606 100644
--- a/arch/x86/virt/svm/cmdline.c
+++ b/arch/x86/virt/svm/cmdline.c
@@ -10,6 +10,7 @@
 #include <linux/string.h>
 #include <linux/printk.h>
 
+#include <asm/cpufeature.h>
 #include <asm/sev.h>
 
 struct sev_config sev_cfg;
@@ -24,6 +25,12 @@ 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