Messages in this thread |  | | Date | Tue, 29 Dec 2020 17:16:41 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return |
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Hi David,
On 2020-12-29 16:00, David Brazdil wrote: > The KVM/arm64 PSCI relay assumes that SYSTEM_OFF and SYSTEM_RESET > should > not return, as dictated by the PSCI spec. However, there is firmware > out > there which breaks this assumption, leading to a hyp panic. Make KVM > more robust to broken firmware by allowing these to return. > > Signed-off-by: David Brazdil <dbrazdil@google.com> > --- > arch/arm64/kvm/hyp/nvhe/psci-relay.c | 13 +++++-------- > 1 file changed, 5 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c > b/arch/arm64/kvm/hyp/nvhe/psci-relay.c > index e3947846ffcb..8e7128cb7667 100644 > --- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c > +++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c > @@ -77,12 +77,6 @@ static unsigned long psci_forward(struct > kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 2), cpu_reg(host_ctxt, 3)); > } > > -static __noreturn unsigned long psci_forward_noreturn(struct > kvm_cpu_context *host_ctxt) > -{ > - psci_forward(host_ctxt); > - hyp_panic(); /* unreachable */ > -} > - > static unsigned int find_cpu_id(u64 mpidr) > { > unsigned int i; > @@ -251,10 +245,13 @@ static unsigned long psci_0_2_handler(u64 > func_id, struct kvm_cpu_context *host_ > case PSCI_0_2_FN_MIGRATE_INFO_TYPE: > case PSCI_0_2_FN64_MIGRATE_INFO_UP_CPU: > return psci_forward(host_ctxt); > + /* > + * SYSTEM_OFF/RESET should not return according to the spec. > + * Allow it so as to stay robust to broken firmware. > + */ > case PSCI_0_2_FN_SYSTEM_OFF: > case PSCI_0_2_FN_SYSTEM_RESET: > - psci_forward_noreturn(host_ctxt); > - unreachable(); > + return psci_forward(host_ctxt); > case PSCI_0_2_FN64_CPU_SUSPEND: > return psci_cpu_suspend(func_id, host_ctxt); > case PSCI_0_2_FN64_CPU_ON:
Thanks for having tracked this.
I wonder whether we should also taint the kernel in this case, because this is completely unexpected, and a major spec violation.
Ideally, we'd be able to detect this case and prevent pKVM from getting initialised at all, but I guess there is no way to detect the sucker without ... calling SYSTEM_RESET?
M. -- Jazz is not dead. It just smells funny...
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