On Fri, Jun 04, 2021 at 03:01:17PM +0100, Mark Rutland wrote:
> 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).
It's not just about the M1, unfortunately. You can boot with:
"kvm-arm.mode=protected id_aa64mmfr1.vh=1"
which will force VHE mode, so we should fail protected mode in that case.
> One minor comment below; otherwise:
>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Thanks, I'll keep the tag but please yell if you want me to drop it.
> > 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.
I'm just moving the existing string here, but as above, it's not M1
specific.
Will
