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Date: Tue, 9 Aug 2022 22:43:59 +0200
From: Eric Auger <eric.auger@...hat.com>
To: Dmytro Maluka <dmy@...ihalf.com>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
Alex Williamson <alex.williamson@...hat.com>,
Rong L Liu <rong.l.liu@...el.com>,
Zhenyu Wang <zhenyuw@...ux.intel.com>,
Tomasz Nowicki <tn@...ihalf.com>,
Grzegorz Jaszczyk <jaz@...ihalf.com>, upstream@...ihalf.com,
Dmitry Torokhov <dtor@...gle.com>,
Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH v2 2/5] KVM: x86: Add
kvm_register_and_fire_irq_mask_notifier()
Hi Dmytro,
On 8/5/22 21:39, Dmytro Maluka wrote:
> In order to implement postponing resamplefd notification until an
> interrupt is unmasked, we need not only to track changes of the
> interrupt mask state (which is already possible with
> kvm_register_irq_mask_notifier()) but also to know its initial
> mask state before any mask notifier has fired.
>
> Moreover, we need to do this initial check of the IRQ mask state in a
> race-free way, to ensure that we will not miss any further mask or
> unmask events after we check the initial mask state.
>
> So implement kvm_register_and_fire_irq_mask_notifier() which atomically
> registers an IRQ mask notifier and calls it with the current mask value
> of the IRQ. It does that using the same locking order as when calling
> notifier normally via kvm_fire_mask_notifiers(), to prevent deadlocks.
>
> Its implementation needs to be arch-specific since it relies on
> arch-specific synchronization (e.g. ioapic->lock and pic->lock on x86,
> or a per-IRQ lock on ARM vGIC) for serializing our initial reading of
> the IRQ mask state with a pending change of this mask state.
>
> For now implement it for x86 only, and for other archs add a weak dummy
> implementation which doesn't really call the notifier (as other archs
> don't currently implement calling notifiers normally via
> kvm_fire_mask_notifiers() either, i.e. registering mask notifiers has no
> effect on those archs anyway).
>
> Signed-off-by: Dmytro Maluka <dmy@...ihalf.com>
> Link: https://lore.kernel.org/lkml/c7b7860e-ae3a-7b98-e97e-28a62470c470@semihalf.com/
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/i8259.c | 6 ++++
> arch/x86/kvm/ioapic.c | 6 ++++
> arch/x86/kvm/ioapic.h | 1 +
> arch/x86/kvm/irq_comm.c | 57 +++++++++++++++++++++++++++++++++
> include/linux/kvm_host.h | 4 +++
> virt/kvm/eventfd.c | 31 ++++++++++++++++--
> 7 files changed, 104 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index dc76617f11c1..cf0571ed2968 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1834,6 +1834,7 @@ static inline int __kvm_irq_line_state(unsigned long *irq_state,
>
> int kvm_pic_set_irq(struct kvm_pic *pic, int irq, int irq_source_id, int level);
> void kvm_pic_clear_all(struct kvm_pic *pic, int irq_source_id);
> +bool kvm_pic_irq_is_masked(struct kvm_pic *s, int irq);
>
> void kvm_inject_nmi(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
> index e1bb6218bb96..1eb3127f6047 100644
> --- a/arch/x86/kvm/i8259.c
> +++ b/arch/x86/kvm/i8259.c
> @@ -211,6 +211,12 @@ void kvm_pic_clear_all(struct kvm_pic *s, int irq_source_id)
> pic_unlock(s);
> }
>
> +/* Called with s->lock held. */
> +bool kvm_pic_irq_is_masked(struct kvm_pic *s, int irq)
> +{
> + return !!(s->pics[irq >> 3].imr & (1 << irq));
> +}
> +
> /*
> * acknowledge interrupt 'irq'
> */
> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> index 765943d7cfa5..fab11de1f885 100644
> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -478,6 +478,12 @@ void kvm_ioapic_clear_all(struct kvm_ioapic *ioapic, int irq_source_id)
> spin_unlock(&ioapic->lock);
> }
>
> +/* Called with ioapic->lock held. */
> +bool kvm_ioapic_irq_is_masked(struct kvm_ioapic *ioapic, int irq)
> +{
> + return !!ioapic->redirtbl[irq].fields.mask;
> +}
> +
> static void kvm_ioapic_eoi_inject_work(struct work_struct *work)
> {
> int i;
> diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
> index 539333ac4b38..fe1f51319992 100644
> --- a/arch/x86/kvm/ioapic.h
> +++ b/arch/x86/kvm/ioapic.h
> @@ -114,6 +114,7 @@ void kvm_ioapic_destroy(struct kvm *kvm);
> int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int irq_source_id,
> int level, bool line_status);
> void kvm_ioapic_clear_all(struct kvm_ioapic *ioapic, int irq_source_id);
> +bool kvm_ioapic_irq_is_masked(struct kvm_ioapic *ioapic, int irq);
> void kvm_get_ioapic(struct kvm *kvm, struct kvm_ioapic_state *state);
> void kvm_set_ioapic(struct kvm *kvm, struct kvm_ioapic_state *state);
> void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu,
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index f27e4c9c403e..4bd4218821a2 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -234,6 +234,63 @@ void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id)
> mutex_unlock(&kvm->irq_lock);
> }
>
> +void kvm_register_and_fire_irq_mask_notifier(struct kvm *kvm, int irq,
> + struct kvm_irq_mask_notifier *kimn)
> +{
> + struct kvm_pic *pic = kvm->arch.vpic;
> + struct kvm_ioapic *ioapic = kvm->arch.vioapic;
> + struct kvm_kernel_irq_routing_entry entries[KVM_NR_IRQCHIPS];
> + struct kvm_kernel_irq_routing_entry *pic_e = NULL, *ioapic_e = NULL;
> + int idx, i, n;
> + bool masked;
> +
> + mutex_lock(&kvm->irq_lock);
> +
> + /*
> + * Not possible to detect if the guest uses the PIC or the
> + * IOAPIC. So assume the interrupt to be unmasked iff it is
> + * unmasked in at least one of both.
> + */
> + idx = srcu_read_lock(&kvm->irq_srcu);
> + n = kvm_irq_map_gsi(kvm, entries, irq);
> + srcu_read_unlock(&kvm->irq_srcu, idx);
> +
> + for (i = 0; i < n; i++) {
> + if (entries[i].type != KVM_IRQ_ROUTING_IRQCHIP)
> + continue;
> +
> + switch (entries[i].irqchip.irqchip) {
> + case KVM_IRQCHIP_PIC_MASTER:
> + case KVM_IRQCHIP_PIC_SLAVE:
> + pic_e = &entries[i];
> + break;
> + case KVM_IRQCHIP_IOAPIC:
> + ioapic_e = &entries[i];
> + break;
> + default:
> + break;
> + }
> + }
> +
> + if (pic_e)
> + spin_lock(&pic->lock);
> + if (ioapic_e)
> + spin_lock(&ioapic->lock);
> +
> + __kvm_register_irq_mask_notifier(kvm, irq, kimn);
> +
> + masked = (!pic_e || kvm_pic_irq_is_masked(pic, pic_e->irqchip.pin)) &&
> + (!ioapic_e || kvm_ioapic_irq_is_masked(ioapic, ioapic_e->irqchip.pin));
Looks a bit cryptic to me. Don't you want pic_e && masked on pic ||
ioapic_e && masked on ioapic?
> + kimn->func(kimn, masked);
> +
> + if (ioapic_e)
> + spin_unlock(&ioapic->lock);
> + if (pic_e)
> + spin_unlock(&pic->lock);
> +
> + mutex_unlock(&kvm->irq_lock);
> +}
> +
> bool kvm_arch_can_set_irq_routing(struct kvm *kvm)
> {
> return irqchip_in_kernel(kvm);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index dd5f14e31996..55233eb18eb4 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1608,8 +1608,12 @@ void kvm_register_irq_ack_notifier(struct kvm *kvm,
> struct kvm_irq_ack_notifier *kian);
> void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
> struct kvm_irq_ack_notifier *kian);
> +void __kvm_register_irq_mask_notifier(struct kvm *kvm, int irq,
> + struct kvm_irq_mask_notifier *kimn);
> void kvm_register_irq_mask_notifier(struct kvm *kvm, int irq,
> struct kvm_irq_mask_notifier *kimn);
> +void kvm_register_and_fire_irq_mask_notifier(struct kvm *kvm, int irq,
> + struct kvm_irq_mask_notifier *kimn);
> void kvm_unregister_irq_mask_notifier(struct kvm *kvm, int irq,
> struct kvm_irq_mask_notifier *kimn);
> void kvm_fire_mask_notifiers(struct kvm *kvm, unsigned irqchip, unsigned pin,
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 39403d9fbdcc..3007d956b626 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -519,15 +519,42 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
> kvm_arch_post_irq_ack_notifier_list_update(kvm);
> }
>
> +void __kvm_register_irq_mask_notifier(struct kvm *kvm, int irq,
> + struct kvm_irq_mask_notifier *kimn)
> +{
> + kimn->irq = irq;
> + hlist_add_head_rcu(&kimn->link, &kvm->irq_mask_notifier_list);
> +}
> +
> void kvm_register_irq_mask_notifier(struct kvm *kvm, int irq,
> struct kvm_irq_mask_notifier *kimn)
> {
> mutex_lock(&kvm->irq_lock);
> - kimn->irq = irq;
> - hlist_add_head_rcu(&kimn->link, &kvm->irq_mask_notifier_list);
> + __kvm_register_irq_mask_notifier(kvm, irq, kimn);
> mutex_unlock(&kvm->irq_lock);
> }
>
> +/*
> + * kvm_register_and_fire_irq_mask_notifier() registers the notifier and
> + * immediately calls it with the current mask value of the IRQ. It does
> + * that atomically, so that we will find out the initial mask state of
> + * the IRQ and will not miss any further mask or unmask events. It does
> + * that using the same locking order as when calling notifier normally
> + * via kvm_fire_mask_notifiers(), to prevent deadlocks.
you may document somewhere that it must be called before
kvm_register_irq_ack_notifier()
> + *
> + * Implementation is arch-specific since it relies on arch-specific
> + * (irqchip-specific) synchronization. Below is a weak dummy
> + * implementation for archs not implementing it yet, as those archs
> + * don't implement calling notifiers normally via
> + * kvm_fire_mask_notifiers() either, i.e. registering mask notifiers
> + * has no effect on those archs anyway.
I would advise you to put Marc in the loop for the whole series (adding
him in CC).
Thanks
Eric
> + */
> +void __weak kvm_register_and_fire_irq_mask_notifier(struct kvm *kvm, int irq,
> + struct kvm_irq_mask_notifier *kimn)
> +{
> + kvm_register_irq_mask_notifier(kvm, irq, kimn);
> +}
> +
> void kvm_unregister_irq_mask_notifier(struct kvm *kvm, int irq,
> struct kvm_irq_mask_notifier *kimn)
> {
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