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).

Reviewed-by: David Brazdil <dbrazdil@google.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Andrew Scull <ascull@google.com>
Link: https://lore.kernel.org/r/20211001170553.3062988-1-maz@kernel.org

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391..f268731 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2365,6 +2365,8 @@
        kvm-arm.mode=
                        [KVM,ARM] Select one of KVM/arm64's modes of operation.
 
+                       none: Forcefully disable KVM.
+
                        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 f8be56d..019490c 100644 (file)
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -58,6 +58,7 @@
 enum kvm_mode {
        KVM_MODE_DEFAULT,
        KVM_MODE_PROTECTED,
+       KVM_MODE_NONE,
 };
 enum kvm_mode kvm_get_mode(void);
 

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index fe102cd..6581712 100644 (file)
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2064,6 +2064,11 @@ 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) ||
@@ -2137,8 +2142,15 @@ 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) {
+               kvm_mode = KVM_MODE_NONE;
+               return 0;
+       }
 
        return -EINVAL;
 }