Messages in this thread | | | Date | Thu, 05 Nov 2020 11:30:44 +0000 | From | Marc Zyngier <> | Subject | Re: [RFC PATCH 18/26] kvm: arm64: Intercept PSCI_CPU_OFF host SMC calls |
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On 2020-11-04 18:36, David Brazdil wrote: > Add a handler of the CPU_OFF PSCI host SMC trapped in KVM nVHE hyp > code. > When invoked, it changes the recorded state of the core to OFF before > forwarding the call to EL3. If the call fails, it changes the state > back > to ON and returns the error to the host. > > Signed-off-by: David Brazdil <dbrazdil@google.com> > --- > arch/arm64/kvm/hyp/nvhe/psci.c | 30 +++++++++++++++++++++++++++++- > 1 file changed, 29 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/nvhe/psci.c > b/arch/arm64/kvm/hyp/nvhe/psci.c > index c3d0a6246c66..00dc0cab860c 100644 > --- a/arch/arm64/kvm/hyp/nvhe/psci.c > +++ b/arch/arm64/kvm/hyp/nvhe/psci.c > @@ -13,6 +13,8 @@ > #include <kvm/arm_psci.h> > #include <uapi/linux/psci.h> > > +#include <nvhe/spinlock.h> > + > /* Config options set by the host. */ > u32 kvm_host_psci_version = PSCI_VERSION(0, 0); > u32 kvm_host_psci_function_id[PSCI_FN_MAX]; > @@ -20,6 +22,7 @@ s64 hyp_physvirt_offset; > > #define __hyp_pa(x) ((phys_addr_t)(x) + hyp_physvirt_offset) > > +static DEFINE_PER_CPU(hyp_spinlock_t, psci_cpu_lock); > DEFINE_PER_CPU(enum kvm_nvhe_psci_state, psci_cpu_state); > > static u64 get_psci_func_id(struct kvm_cpu_context *host_ctxt) > @@ -76,9 +79,32 @@ static __noreturn unsigned long > psci_forward_noreturn(struct kvm_cpu_context *ho > hyp_panic(); /* unreachable */ > } > > +static int psci_cpu_off(u64 func_id, struct kvm_cpu_context > *host_ctxt) > +{ > + hyp_spinlock_t *cpu_lock = this_cpu_ptr(&psci_cpu_lock); > + enum kvm_nvhe_psci_state *cpu_power = this_cpu_ptr(&psci_cpu_state); > + u32 power_state = (u32)host_ctxt->regs.regs[1]; > + int ret; > + > + /* Change the recorded state to OFF before forwarding the call. */ > + hyp_spin_lock(cpu_lock); > + *cpu_power = KVM_NVHE_PSCI_CPU_OFF; > + hyp_spin_unlock(cpu_lock);
So at this point, another CPU can observe the vcpu being "off", and issue a PSCI_ON, which may result in an "already on". I'm not sure this is an actual issue, but it is worth documenting.
What is definitely missing is a rational about *why* we need to track the state of the vcpus. I naively imagined that we could directly proxy the PSCI calls to EL3, only repainting PC for PSCI_ON.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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