On Thu, Jun 03, 2021 at 07:33:44PM +0100, Will Deacon wrote:
> Ignore 'kvm-arm.mode=protected' when using VHE so that kvm_get_mode()
> only returns KVM_MODE_PROTECTED on systems where the feature is available.
IIUC, since the introduction of the idreg-override code, and the
mutate_to_vhe stuff, passing 'kvm-arm.mode=protected' should make the
kernel stick to EL1, right? So this should only affect M1 (or other HW
with a similar impediment).
One minor comment below; otherwise:
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
>
> Cc: David Brazdil <dbrazdil@xxxxxxxxxx>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 1 -
> arch/arm64/kernel/cpufeature.c | 10 +---------
> arch/arm64/kvm/arm.c | 6 +++++-
> 3 files changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cb89dbdedc46..e85dbdf1ee8e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2300,7 +2300,6 @@
>
> protected: nVHE-based mode with support for guests whose
> state is kept private from the host.
> - Not valid if the kernel is running in EL2.
>
> Defaults to VHE/nVHE based on hardware support.
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index efed2830d141..dc1f2e747828 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1773,15 +1773,7 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
> #ifdef CONFIG_KVM
> static bool is_kvm_protected_mode(const struct arm64_cpu_capabilities *entry, int __unused)
> {
> - if (kvm_get_mode() != KVM_MODE_PROTECTED)
> - return false;
> -
> - if (is_kernel_in_hyp_mode()) {
> - pr_warn("Protected KVM not available with VHE\n");
> - return false;
> - }
> -
> - return true;
> + return kvm_get_mode() == KVM_MODE_PROTECTED;
> }
> #endif /* CONFIG_KVM */
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 1cb39c0803a4..8d5e23198dfd 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2121,7 +2121,11 @@ static int __init early_kvm_mode_cfg(char *arg)
> return -EINVAL;
>
> if (strcmp(arg, "protected") == 0) {
> - kvm_mode = KVM_MODE_PROTECTED;
> + if (!is_kernel_in_hyp_mode())
> + kvm_mode = KVM_MODE_PROTECTED;
> + else
> + pr_warn_once("Protected KVM not available with VHE\n");
... assuming this is only for M1, it might be better to say:
Protected KVM not available on this hardware
... since that doesn't suggest that other VHE-capable HW is also not
PKVM-capable.
Thanks,
Mark.
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