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x86/virt: Provide "nosnp" boot option for sev kernel command line

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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: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Pavan Kumar Paluri <papaluri@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20241014130948.1476946-3-papaluri@amd.com
This commit is contained in:
Pavan Kumar Paluri 2024-10-14 08:09:48 -05:00 committed by Borislav Petkov (AMD)
parent 4ae47fa7e8
commit 2db67aaca5
2 changed files with 17 additions and 0 deletions
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5
Documentation/arch/x86/x86_64/boot-options.rst
View File

@ -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.

12
arch/x86/virt/svm/cmdline.c
View File

@ -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);
}