Commit 2db67aac authored by Pavan Kumar Paluri's avatar Pavan Kumar Paluri Committed by Borislav Petkov (AMD)
Browse files

x86/virt: 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.

  [ bp: Actually make it a HV-only cmdline option. ]

Co-developed-by: default avatarEric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: default avatarEric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: default avatarPavan Kumar Paluri <papaluri@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20241014130948.1476946-3-papaluri@amd.com
parent 4ae47fa7

Documentation/arch/x86/x86_64/boot-options.rst

+5 −0
Original line number Diff line number Diff line
@@ -305,3 +305,8 @@ The available options are: 


   debug

     Enable debug messages.



   nosnp

     Do not enable SEV-SNP (applies to host/hypervisor only). Setting

     'nosnp' avoids the RMP check overhead in memory accesses when

     users do not want to run SEV-SNP guests.

arch/x86/virt/svm/cmdline.c

+12 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/string.h>

#include <linux/printk.h>

#include <linux/cache.h>

#include <linux/cpufeature.h>



#include <asm/sev-common.h>
@@ -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);

	}