From ce0abef6a1d540acef85068e0e82bdf1fbeeb0e9 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 19 Apr 2024 17:05:55 -0700 Subject: cpu: Ignore "mitigations" kernel parameter if CPU_MITIGATIONS=n Explicitly disallow enabling mitigations at runtime for kernels that were built with CONFIG_CPU_MITIGATIONS=n, as some architectures may omit code entirely if mitigations are disabled at compile time. E.g. on x86, a large pile of Kconfigs are buried behind CPU_MITIGATIONS, and trying to provide sane behavior for retroactively enabling mitigations is extremely difficult, bordering on impossible. E.g. page table isolation and call depth tracking require build-time support, BHI mitigations will still be off without additional kernel parameters, etc. [ bp: Touchups. ] Signed-off-by: Sean Christopherson Signed-off-by: Borislav Petkov (AMD) Acked-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20240420000556.2645001-3-seanjc@google.com --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ 1 file changed, 3 insertions(+) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 902ecd92a29f..213d0719e2b7 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3423,6 +3423,9 @@ arch-independent options, each of which is an aggregation of existing arch-specific options. + Note, "mitigations" is supported if and only if the + kernel was built with CPU_MITIGATIONS=y. + off Disable all optional CPU mitigations. This improves system performance, but it may also -- cgit v1.2.3