From 5b63fb56a85c960aaf0aab6c1eec47bf3df94bf9 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Fri, 3 Sep 2021 10:16:52 +0100 Subject: [PATCH] FROMLIST: KVM: arm64: Allow KVM to be disabled from the command line Although KVM can be compiled out of the kernel, it cannot be disabled at runtime. Allow this possibility by introducing a new mode that will prevent KVM from initialising. This is useful in the (limited) circumstances where you don't want KVM to be available (what is wrong with you?), or when you want to install another hypervisor instead (good luck with that). Bug: 192819132 Test: boot in EL2, pass kvm-arm.mode=none on cmdline Link: https://lore.kernel.org/kvmarm/20210903091652.985836-1-maz@kernel.org/ Signed-off-by: Marc Zyngier Change-Id: If4d2775b8f1f4119b5f390391f64c65221a17fde --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kernel/idreg-override.c | 1 + arch/arm64/kvm/arm.c | 14 +++++++++++++- 4 files changed, 18 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 4223a4ba2ea0..69804b20833f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2302,6 +2302,9 @@ kvm-arm.mode= [KVM,ARM] Select one of KVM/arm64's modes of operation. + none: Forcefully disable KVM and run in nVHE mode, + preventing KVM from ever initialising. + nvhe: Standard nVHE-based mode, without support for protected guests. diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index b45ae346301a..d276bc897ad9 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -59,6 +59,7 @@ enum kvm_mode { KVM_MODE_DEFAULT, KVM_MODE_PROTECTED, + KVM_MODE_NONE, }; enum kvm_mode kvm_get_mode(void); diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c index f2f6f4150bdc..3ef853a792f3 100644 --- a/arch/arm64/kernel/idreg-override.c +++ b/arch/arm64/kernel/idreg-override.c @@ -94,6 +94,7 @@ static const struct { char alias[FTR_ALIAS_NAME_LEN]; char feature[FTR_ALIAS_OPTION_LEN]; } aliases[] __initconst = { + { "kvm-arm.mode=none", "id_aa64mmfr1.vh=0" }, { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" }, { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" }, { "arm64.nobti", "id_aa64pfr1.bt=0" }, diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index de81ec8df665..d0688ceaccf0 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -2046,6 +2046,11 @@ int kvm_arch_init(void *opaque) return -ENODEV; } + if (kvm_get_mode() == KVM_MODE_NONE) { + kvm_info("KVM disabled from command line\n"); + return -ENODEV; + } + in_hyp_mode = is_kernel_in_hyp_mode(); if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) || @@ -2119,8 +2124,15 @@ static int __init early_kvm_mode_cfg(char *arg) return 0; } - if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) + if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) { + kvm_mode = KVM_MODE_DEFAULT; return 0; + } + + if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) { + kvm_mode = KVM_MODE_NONE; + return 0; + } return -EINVAL; }