mn Fri, Jun 30, 2023, Chao Gao wrote:
> On Fri, Jun 30, 2023 at 03:26:12PM +0800, Qi Ai wrote:
> >+ !is_protmode(vcpu))
> >+ kvm_x86_ops.clear_hlt(vcpu);
>
> Use static_call_cond(kvm_x86_clear_hlt)(vcpu) instead.
>
> It looks incorrect that we add this side-effect heuristically here. I
Yeah, adding heuristics to KVM_SET_REGS isn't happening. KVM's existing hack
for "Older userspace" in __set_sregs_common() is bad enough:
/* Older userspace won't unhalt the vcpu on reset. */
if (kvm_vcpu_is_bsp(vcpu) && kvm_rip_read(vcpu) == 0xfff0 &&
sregs->cs.selector == 0xf000 && sregs->cs.base == 0xffff0000 &&
!is_protmode(vcpu))
vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
> am wondering if we can link vcpu->arch.mp_state to VMCS activity state,
Hrm, maybe.
> i.e., when mp_state is set to RUNNABLE in KVM_SET_MP_STATE ioctl, KVM
> sets VMCS activity state to active.
Not in the ioctl(), there needs to be a proper set of APIs, e.g. so that the
existing hack works, and so that KVM actually reports out to userspace that a
vCPU is HALTED if userspace gained control of the vCPU, e.g. after an IRQ exit,
while the vCPU was HALTED. I.e. mp_state versus vmcs.ACTIVITY_STATE needs to be
bidirectional, not one-way. E.g. if a vCPU is live migrated, I'm pretty sure
vmcs.ACTIVITY_STATE is lost, which is wrong.
The downside is that if KVM propagates vmcs.ACTIVITY_STATE to mp_state for the
halted case, then KVM will enter kvm_vcpu_halt() instead of entering the guest
in halted state, which is undesirable. Hmm, that can be handled by treating
the vCPU as running, e.g.
static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
{
return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE ||
(vcpu->arch.mp_state == KVM_MP_STATE_HALTED &&
kvm_hlt_in_guest(vcpu->kvm))) &&
!vcpu->arch.apf.halted);
}
but that would have cascading effect to a whole pile of things. I don't *think*
they'd be used with kvm_hlt_in_guest(), but we've had weirder stuff.
I'm half tempted to solve this particular issue by stuffing vmcs.ACTIVITY_STATE on
shutdown, similar to what SVM does on shutdown interception. KVM doesn't come
anywhere near faithfully emulating shutdown, so it's unlikely to break anything.
And then the mp_state vs. hlt_in_guest coulbe tackled separately. Ugh, but that
wouldn't cover a synthesized KVM_REQ_TRIPLE_FAULT.
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 44fb619803b8..ee4bb37067d1 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5312,6 +5312,8 @@ static __always_inline int handle_external_interrupt(struct kvm_vcpu *vcpu)
static int handle_triple_fault(struct kvm_vcpu *vcpu)
{
+ vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
+
vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
vcpu->mmio_needed = 0;
return 0;
I don't suppose QEMU can to blast INIT at all vCPUs for this case?
