Message-ID: <CAJHc60wn=vA9j421FhVkMqYc0w8u2ZYuc-9TJ+rvriSXjseKHw@mail.gmail.com>
Date: Mon, 28 Oct 2024 09:43:45 -0700
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	stable@...r.kernel.org, syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH] KVM: arm64: Mark the VM as dead for failed initializations

Hi Oliver,


On Sat, Oct 26, 2024 at 7:53 AM Oliver Upton <oliver.upton@...ux.dev> wrote:
>
> On Sat, Oct 26, 2024 at 08:43:21AM +0100, Marc Zyngier wrote:
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index bf64fed9820e..c315bc1a4e9a 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -74,8 +74,6 @@ enum kvm_mode kvm_get_mode(void);
> >  static inline enum kvm_mode kvm_get_mode(void) { return KVM_MODE_NONE; };
> >  #endif
> >
> > -DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
> > -
> >  extern unsigned int __ro_after_init kvm_sve_max_vl;
> >  extern unsigned int __ro_after_init kvm_host_sve_max_vl;
> >  int __init kvm_arm_init_sve(void);
> > diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> > index 879982b1cc73..1215df590418 100644
> > --- a/arch/arm64/kvm/arch_timer.c
> > +++ b/arch/arm64/kvm/arch_timer.c
> > @@ -206,8 +206,7 @@ void get_timer_map(struct kvm_vcpu *vcpu, struct timer_map *map)
> >
> >  static inline bool userspace_irqchip(struct kvm *kvm)
> >  {
> > -     return static_branch_unlikely(&userspace_irqchip_in_use) &&
> > -             unlikely(!irqchip_in_kernel(kvm));
> > +     return unlikely(!irqchip_in_kernel(kvm));
> >  }
> >
> >  static void soft_timer_start(struct hrtimer *hrt, u64 ns)
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 48cafb65d6ac..70ff9a20ef3a 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -69,7 +69,6 @@ DECLARE_KVM_NVHE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
> >  static bool vgic_present, kvm_arm_initialised;
> >
> >  static DEFINE_PER_CPU(unsigned char, kvm_hyp_initialized);
> > -DEFINE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
> >
> >  bool is_kvm_arm_initialised(void)
> >  {
> > @@ -503,9 +502,6 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
> >
> >  void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
> >  {
> > -     if (vcpu_has_run_once(vcpu) && unlikely(!irqchip_in_kernel(vcpu->kvm)))
> > -             static_branch_dec(&userspace_irqchip_in_use);
> > -
> >       kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
> >       kvm_timer_vcpu_terminate(vcpu);
> >       kvm_pmu_vcpu_destroy(vcpu);
> > @@ -848,14 +844,6 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
> >                       return ret;
> >       }
> >
> > -     if (!irqchip_in_kernel(kvm)) {
> > -             /*
> > -              * Tell the rest of the code that there are userspace irqchip
> > -              * VMs in the wild.
> > -              */
> > -             static_branch_inc(&userspace_irqchip_in_use);
> > -     }
> > -
> >       /*
> >        * Initialize traps for protected VMs.
> >        * NOTE: Move to run in EL2 directly, rather than via a hypercall, once
> > @@ -1077,7 +1065,7 @@ static bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu, int *ret)
> >        * state gets updated in kvm_timer_update_run and
> >        * kvm_pmu_update_run below).
> >        */
> > -     if (static_branch_unlikely(&userspace_irqchip_in_use)) {
> > +     if (unlikely(!irqchip_in_kernel(vcpu->kvm))) {
> >               if (kvm_timer_should_notify_user(vcpu) ||
> >                   kvm_pmu_should_notify_user(vcpu)) {
> >                       *ret = -EINTR;
> > @@ -1199,7 +1187,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
> >                       vcpu->mode = OUTSIDE_GUEST_MODE;
> >                       isb(); /* Ensure work in x_flush_hwstate is committed */
> >                       kvm_pmu_sync_hwstate(vcpu);
> > -                     if (static_branch_unlikely(&userspace_irqchip_in_use))
> > +                     if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
> >                               kvm_timer_sync_user(vcpu);
> >                       kvm_vgic_sync_hwstate(vcpu);
> >                       local_irq_enable();
> > @@ -1245,7 +1233,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
> >                * we don't want vtimer interrupts to race with syncing the
> >                * timer virtual interrupt state.
> >                */
> > -             if (static_branch_unlikely(&userspace_irqchip_in_use))
> > +             if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
> >                       kvm_timer_sync_user(vcpu);
> >
> >               kvm_arch_vcpu_ctxsync_fp(vcpu);
> >
> > I think this would fix the problem you're seeing without changing the
> > userspace view of an erroneous configuration. It would also pave the
> > way for the complete removal of the interrupt notification to
> > userspace, which I claim has no user and is just a shit idea.
>
> Yeah, looks like this ought to get it done.
>
> Even with a fix for this particular issue I do wonder if we should
> categorically harden against late initialization failures and un-init
> the vCPU (or bug VM, where necessary) to avoid dealing with half-baked
> vCPUs/VMs across our UAPI surfaces.
>
> A sane userspace will probably crash when KVM_RUN returns EINVAL anyway.

Thanks for the suggestion. Sure, I'll take another look at the
possible things that we can uninitialize and try to re-spin the patch.

Marc,

If you feel userspace_irqchip_in_use is not necessary anymore, and as
a quick fix to this issue, we can get rid of that independent of the
un-init effort.

Thank you.
Raghavendra

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