Message-ID: <4C47D147-A186-45D4-B474-46C209D87F2A@nutanix.com>
Date: Fri, 16 Jan 2026 04:41:20 +0000
From: Khushit Shah <khushit.shah@...anix.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: David Woodhouse <dwmw2@...radead.org>,
        "pbonzini@...hat.com"
	<pbonzini@...hat.com>,
        "kai.huang@...el.com" <kai.huang@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        Jon
 Kohler <jon@...anix.com>,
        Shaju Abraham <shaju.abraham@...anix.com>
Subject: Re: [PATCH v5 1/3] KVM: x86: Refactor suppress EOI broadcast logic



> On 14 Jan 2026, at 5:40 AM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> case APIC_SPIV: {
> u32 mask = 0x3ff;
> if (kvm_lapic_get_reg(apic, APIC_LVR) & APIC_LVR_DIRECTED_EOI)
> mask |= APIC_SPIV_DIRECTED_EOI;
> apic_set_spiv(apic, val & mask);
> if (!(val & APIC_SPIV_APIC_ENABLED)) {
> int i;
> 
> for (i = 0; i < apic->nr_lvt_entries; i++) {
> kvm_lapic_set_reg(apic, APIC_LVTx(i),
> kvm_lapic_get_reg(apic, APIC_LVTx(i)) | APIC_LVT_MASKED);
> }
> apic_update_lvtt(apic);
> atomic_set(&apic->lapic_timer.pending, 0);
> 
> }
> break;
> }
> 
> It _is_ possible for the virtual APIC to end up with the bit set, because KVM
> doesn't sanitize APIC_SPIV during kvm_apic_set_state().

Ohh Wow! Okay. 

> On 14 Jan 2026, at 5:40 AM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> Except that it needs to work when it's re-enabled in a few patches.  And as per
> commit c806a6ad35bf ("KVM: x86: call irq notifiers with directed EOI") and
> https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.kernel.org_show-5Fbug.cgi-3Fid-3D82211&d=DwIFaQ&c=s883GpUCOChKOHiocYtGcg&r=PGWMyignA0NiDmTlyP7vOTHozBws_VN86yrVmSMkBp0&m=3a8aRAaT-5-y7XGNZDSigpCoMKWgZMPHgKMf0pNKs-BEnjmuhtg8NxX9-jSx6CTp&s=qRth9VSXr8AqIx-tfKzLf8j4Fks5TtSdUMHhre4cgAo&e= , allegedly KVM needs to notify
> listeners in this case.
> 
> Given that KVM didn't actually implement Directed EOI in the in-kernel I/O APIC,
> it's certainly debatable as to whether or not that still holds true, i.e. it may
> have been a misdiagnosed root cause.  But I have zero interest in finding out
> the hard way, especially since the in-kernel I/O APIC is slowly being deprecated,
> and _especially_ not in patches that will be Cc'd stable.
> 
> So while I agree it would be nice to simultaneously enable the in-kernel I/O APIC,
> I want to prioritize landing the fix for split IRQCHIP.  And if we're clever,
> enabling in-kernel I/O APIC support in the future shouldn't require any new uAPI,
> since we can document the limitation and not advertise
> KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST in KVM_CAP_X2APIC_API when run on a VM
> without a split IRQCHIP.  Then if support is ever added broadly, we can drop the
> relevant code that requires irqchip_split() and update the documentation to say
> that userspace need to query KVM_CAP_X2APIC_API on a VM fd to determine whether
> or not the flag is supported for an in-kernel I/O APIC.
> 
> If someone has a strong need and use case for supporting Supress EOI Broadcast for
> an in-kernel I/O APIC, then they can have the honor of proving that things like
> Windows and Xen play nice with KVM's implementation.  And they can do that on top.

I agree on not finding it the hard way. I am okay with prioritising fix for split IRQCHIP.




> On 14 Jan 2026, at 5:40 AM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> --
> From: Khushit Shah <khushit.shah@...anix.com>
> Date: Mon, 29 Dec 2025 11:17:06 +0000
> Subject: [PATCH] KVM: x86: Add x2APIC "features" to control EOI broadcast
> suppression
> 
> Add two flags for KVM_CAP_X2APIC_API to allow userspace to control support
> for Suppress EOI Broadcasts when using a split IRQCHIP (I/O APIC emulated
> by userspace), which KVM completely mishandles. When x2APIC support was
> first added, KVM incorrectly advertised and "enabled" Suppress EOI
> Broadcast, without fully supporting the I/O APIC side of the equation,
> i.e. without adding directed EOI to KVM's in-kernel I/O APIC.
> 
> That flaw was carried over to split IRQCHIP support, i.e. KVM advertised
> support for Suppress EOI Broadcasts irrespective of whether or not the
> userspace I/O APIC implementation supported directed EOIs. Even worse,
> KVM didn't actually suppress EOI broadcasts, i.e. userspace VMMs without
> support for directed EOI came to rely on the "spurious" broadcasts.
> 
> KVM "fixed" the in-kernel I/O APIC implementation by completely disabling
> support for Suppress EOI Broadcasts in commit 0bcc3fb95b97 ("KVM: lapic:
> stop advertising DIRECTED_EOI when in-kernel IOAPIC is in use"), but
> didn't do anything to remedy userspace I/O APIC implementations.
> 
> KVM's bogus handling of Suppress EOI Broadcast is problematic when the
> guest relies on interrupts being masked in the I/O APIC until well after
> the initial local APIC EOI. E.g. Windows with Credential Guard enabled
> handles interrupts in the following order:
>  1. Interrupt for L2 arrives.
>  2. L1 APIC EOIs the interrupt.
>  3. L1 resumes L2 and injects the interrupt.
>  4. L2 EOIs after servicing.
>  5. L1 performs the I/O APIC EOI.
> 
> Because KVM EOIs the I/O APIC at step #2, the guest can get an interrupt
> storm, e.g. if the IRQ line is still asserted and userspace reacts to the
> EOI by re-injecting the IRQ, because the guest doesn't de-assert the line
> until step #4, and doesn't expect the interrupt to be re-enabled until
> step #5.
> 
> Unfortunately, simply "fixing" the bug isn't an option, as KVM has no way
> of knowing if the userspace I/O APIC supports directed EOIs, i.e.
> suppressing EOI broadcasts would result in interrupts being stuck masked
> in the userspace I/O APIC due to step #5 being ignored by userspace. And
> fully disabling support for Suppress EOI Broadcast is also undesirable, as
> picking up the fix would require a guest reboot, *and* more importantly
> would change the virtual CPU model exposed to the guest without any buy-in
> from userspace.
> 
> Add KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST and
> KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST flags to allow userspace to
> explicitly enable or disable support for Suppress EOI Broadcasts. This
> gives userspace control over the virtual CPU model exposed to the guest,
> as KVM should never have enabled support for Suppress EOI Broadcast without
> userspace opt-in. Not setting either flag will result in legacy quirky
> behavior for backward compatibility.
> 
> Disallow fully enabling SUPPRESS_EOI_BROADCAST when using an in-kernel
> I/O APIC, as KVM's history/support is just as tragic.  E.g. it's not clear
> that commit c806a6ad35bf ("KVM: x86: call irq notifiers with directed EOI")
> was entirely correct, i.e. it may have simply papered over the lack of
> Directed EOI emulation in the I/O APIC.
> 
> Note, Suppress EOI Broadcasts is defined only in Intel's SDM, not in AMD's
> APM. But the bit is writable on some AMD CPUs, e.g. Turin, and KVM's ABI
> is to support Directed EOI (KVM's name) irrespective of guest CPU vendor.
> 
> Fixes: 7543a635aa09 ("KVM: x86: Add KVM exit for IOAPIC EOIs")
> Closes: https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_kvm_7D497EF1-2D607D-2D4D37-2D98E7-2DDAF95F099342-40nutanix.com&d=DwIFaQ&c=s883GpUCOChKOHiocYtGcg&r=PGWMyignA0NiDmTlyP7vOTHozBws_VN86yrVmSMkBp0&m=3a8aRAaT-5-y7XGNZDSigpCoMKWgZMPHgKMf0pNKs-BEnjmuhtg8NxX9-jSx6CTp&s=KnIT5Yo-kg0bFDhJahB2sRZX445TmPKS4mmCSM0vhqo&e=
> Cc: stable@...r.kernel.org
> Suggested-by: David Woodhouse <dwmw2@...radead.org>
> Signed-off-by: Khushit Shah <khushit.shah@...anix.com>
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> Documentation/virt/kvm/api.rst  | 28 +++++++++++-
> arch/x86/include/asm/kvm_host.h |  7 +++
> arch/x86/include/uapi/asm/kvm.h |  6 ++-
> arch/x86/kvm/ioapic.c           |  2 +-
> arch/x86/kvm/lapic.c            | 76 +++++++++++++++++++++++++++++----
> arch/x86/kvm/lapic.h            |  2 +
> arch/x86/kvm/x86.c              | 21 ++++++++-
> 7 files changed, 127 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 01a3abef8abb..f1f1d2e5dc7c 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -7835,8 +7835,10 @@ Will return -EBUSY if a VCPU has already been created.
> 
> Valid feature flags in args[0] are::
> 
> -  #define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)
> -  #define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK  (1ULL << 1)
> +  #define KVM_X2APIC_API_USE_32BIT_IDS               (1ULL << 0)
> +  #define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK      (1ULL << 1)
> +  #define KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST              (1ULL << 2)
> +  #define KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST             (1ULL << 3)
> 
> Enabling KVM_X2APIC_API_USE_32BIT_IDS changes the behavior of
> KVM_SET_GSI_ROUTING, KVM_SIGNAL_MSI, KVM_SET_LAPIC, and KVM_GET_LAPIC,
> @@ -7849,6 +7851,28 @@ as a broadcast even in x2APIC mode in order to support physical x2APIC
> without interrupt remapping.  This is undesirable in logical mode,
> where 0xff represents CPUs 0-7 in cluster 0.
> 
> +Setting KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST instructs KVM to enable
> +Suppress EOI Broadcasts.  KVM will advertise support for Suppress EOI
> +Broadcast to the guest and suppress LAPIC EOI broadcasts when the guest
> +sets the Suppress EOI Broadcast bit in the SPIV register.  This flag is
> +supported only when using a split IRQCHIP.
> +
> +Setting KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST disables support for
> +Suppress EOI Broadcasts entirely, i.e. instructs KVM to NOT advertise
> +support to the guest.
> +
> +Modern VMMs should either enable KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST
> +or KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST.  If not, legacy quirky
> +behavior will be used by KVM: in split IRQCHIP mode, KVM will advertise
> +support for Suppress EOI Broadcasts but not actually suppress EOI
> +broadcasts; for in-kernel IRQCHIP mode, KVM will not advertise support for
> +Suppress EOI Broadcasts.
> +
> +Setting both KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST and
> +KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST will fail with an EINVAL error,
> +as will setting KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST without a split
> +IRCHIP.
> +
> 7.8 KVM_CAP_S390_USER_INSTR0
> ----------------------------
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ecd4019b84b7..125bd9a4b807 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1238,6 +1238,12 @@ enum kvm_irqchip_mode {
> KVM_IRQCHIP_SPLIT,        /* created with KVM_CAP_SPLIT_IRQCHIP */
> };
> 
> +enum kvm_suppress_eoi_broadcast_mode {
> + KVM_SUPPRESS_EOI_BROADCAST_QUIRKED, /* Legacy behavior */
> + KVM_SUPPRESS_EOI_BROADCAST_ENABLED, /* Enable Suppress EOI broadcast */
> + KVM_SUPPRESS_EOI_BROADCAST_DISABLED /* Disable Suppress EOI broadcast */
> +};
> +
> struct kvm_x86_msr_filter {
> u8 count;
> bool default_allow:1;
> @@ -1487,6 +1493,7 @@ struct kvm_arch {
> 
> bool x2apic_format;
> bool x2apic_broadcast_quirk_disabled;
> + enum kvm_suppress_eoi_broadcast_mode suppress_eoi_broadcast_mode;
> 
> bool has_mapped_host_mmio;
> bool guest_can_read_msr_platform_info;
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index 7ceff6583652..1b0ad5440b99 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -914,8 +914,10 @@ struct kvm_sev_snp_launch_finish {
> __u64 pad1[4];
> };
> 
> -#define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)
> -#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK  (1ULL << 1)
> +#define KVM_X2APIC_API_USE_32BIT_IDS (_BITULL(0))
> +#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK (_BITULL(1))
> +#define KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST (_BITULL(2))
> +#define KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST (_BITULL(3))
> 
> struct kvm_hyperv_eventfd {
> __u32 conn_id;
> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> index 9a99d01b111c..a38a8e2ac70b 100644
> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -555,7 +555,7 @@ static void kvm_ioapic_update_eoi_one(struct kvm_vcpu *vcpu,
> spin_lock(&ioapic->lock);
> 
> if (trigger_mode != IOAPIC_LEVEL_TRIG ||
> -     kvm_lapic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI)
> +     kvm_lapic_suppress_eoi_broadcast(apic))
> return;
> 
> ent->fields.remote_irr = 0;
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 78c39341b2a5..c175a021e1a9 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -105,6 +105,63 @@ bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector)
> apic_test_vector(vector, apic->regs + APIC_IRR);
> }
> 
> +static bool kvm_lapic_advertise_suppress_eoi_broadcast(struct kvm *kvm)
> +{
> + switch (kvm->arch.suppress_eoi_broadcast_mode) {
> + case KVM_SUPPRESS_EOI_BROADCAST_ENABLED:
> + return true;
> + case KVM_SUPPRESS_EOI_BROADCAST_DISABLED:
> + return false;
> + case KVM_SUPPRESS_EOI_BROADCAST_QUIRKED:
> + /*
> +  * The default in-kernel I/O APIC emulates the 82093AA and does not
> +  * implement an EOI register. Some guests (e.g. Windows with the
> +  * Hyper-V role enabled) disable LAPIC EOI broadcast without
> +  * checking the I/O APIC version, which can cause level-triggered
> +  * interrupts to never be EOI'd.
> +  *
> +  * To avoid this, KVM doesn't advertise Suppress EOI Broadcast
> +  * support when using the default in-kernel I/O APIC.
> +  *
> +  * Historically, in split IRQCHIP mode, KVM always advertised
> +  * Suppress EOI Broadcast support but did not actually suppress
> +  * EOIs, resulting in quirky behavior.
> +  */
> + return !ioapic_in_kernel(kvm);
> + default:
> + WARN_ON_ONCE(1);
> + return false;
> + }
> +}
> +
> +bool kvm_lapic_suppress_eoi_broadcast(struct kvm_lapic *apic)
> +{
> + struct kvm *kvm = apic->vcpu->kvm;
> +
> + if (!(kvm_lapic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI))
> + return false;
> +
> + switch (kvm->arch.suppress_eoi_broadcast_mode) {
> + case KVM_SUPPRESS_EOI_BROADCAST_ENABLED:
> + return true;
> + case KVM_SUPPRESS_EOI_BROADCAST_DISABLED:
> + return false;
> + case KVM_SUPPRESS_EOI_BROADCAST_QUIRKED:
> + /*
> +  * Historically, in split IRQCHIP mode, KVM ignored the suppress
> +  * EOI broadcast bit set by the guest and broadcasts EOIs to the
> +  * userspace I/O APIC. For In-kernel I/O APIC, the support itself
> +  * is not advertised, can only be enabled KVM_SET_APIC_STATE, and
> +  * and KVM's I/O APIC doesn't emulate Directed EOIs; but if the
> +  * feature is enabled, it is respected (with odd behavior).
> +  */
> + return ioapic_in_kernel(kvm);
> + default:
> + WARN_ON_ONCE(1);
> + return false;
> + }
> +}
> +
> __read_mostly DEFINE_STATIC_KEY_FALSE(kvm_has_noapic_vcpu);
> EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_has_noapic_vcpu);
> 
> @@ -554,15 +611,9 @@ void kvm_apic_set_version(struct kvm_vcpu *vcpu)
> 
> v = APIC_VERSION | ((apic->nr_lvt_entries - 1) << 16);
> 
> - /*
> -  * KVM emulates 82093AA datasheet (with in-kernel IOAPIC implementation)
> -  * which doesn't have EOI register; Some buggy OSes (e.g. Windows with
> -  * Hyper-V role) disable EOI broadcast in lapic not checking for IOAPIC
> -  * version first and level-triggered interrupts never get EOIed in
> -  * IOAPIC.
> -  */
> +
> if (guest_cpu_cap_has(vcpu, X86_FEATURE_X2APIC) &&
> -     !ioapic_in_kernel(vcpu->kvm))
> +     kvm_lapic_advertise_suppress_eoi_broadcast(vcpu->kvm))
> v |= APIC_LVR_DIRECTED_EOI;
> kvm_lapic_set_reg(apic, APIC_LVR, v);
> }
> @@ -1517,6 +1568,15 @@ static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
> 
> /* Request a KVM exit to inform the userspace IOAPIC. */
> if (irqchip_split(apic->vcpu->kvm)) {
> + /*
> +  * Don't exit to userspace if the guest has enabled Directed
> +  * EOI, a.k.a. Suppress EOI Broadcasts, in which case the local
> +  * APIC doesn't broadcast EOIs (the guest must EOI the target
> +  * I/O APIC(s) directly).
> +  */
> + if (kvm_lapic_suppress_eoi_broadcast(apic))
> + return;
> +
> apic->vcpu->arch.pending_ioapic_eoi = vector;
> kvm_make_request(KVM_REQ_IOAPIC_EOI_EXIT, apic->vcpu);
> return;
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 71c80fa020e0..cf8aed8c95ea 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -239,6 +239,8 @@ static inline int kvm_lapic_latched_init(struct kvm_vcpu *vcpu)
> 
> bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector);
> 
> +bool kvm_lapic_suppress_eoi_broadcast(struct kvm_lapic *apic);
> +
> void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu);
> 
> void kvm_bitmap_or_dest_vcpus(struct kvm *kvm, struct kvm_lapic_irq *irq,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3d4e07f9cff5..82d893d262fa 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -121,8 +121,10 @@ static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
> 
> #define KVM_CAP_PMU_VALID_MASK KVM_PMU_CAP_DISABLE
> 
> -#define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_IDS | \
> -                                    KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)
> +#define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_IDS |  \
> +     KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK | \
> +     KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST | \
> +     KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST)
> 
> static void update_cr8_intercept(struct kvm_vcpu *vcpu);
> static void process_nmi(struct kvm_vcpu *vcpu);
> @@ -4943,6 +4945,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> break;
> case KVM_CAP_X2APIC_API:
> r = KVM_X2APIC_API_VALID_FLAGS;
> + if (kvm && !irqchip_split(kvm))
> + r &= ~KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST;
> break;
> case KVM_CAP_NESTED_STATE:
> r = kvm_x86_ops.nested_ops->get_state ?
> @@ -6751,11 +6755,24 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> if (cap->args[0] & ~KVM_X2APIC_API_VALID_FLAGS)
> break;
> 
> + if ((cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST) &&
> +     (cap->args[0] & KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST))
> + break;
> +
> + if ((cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST) &&
> +     !irqchip_split(kvm))
> + break;
> +
> if (cap->args[0] & KVM_X2APIC_API_USE_32BIT_IDS)
> kvm->arch.x2apic_format = true;
> if (cap->args[0] & KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)
> kvm->arch.x2apic_broadcast_quirk_disabled = true;
> 
> + if (cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST)
> + kvm->arch.suppress_eoi_broadcast_mode = KVM_SUPPRESS_EOI_BROADCAST_ENABLED;
> + if (cap->args[0] & KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST)
> + kvm->arch.suppress_eoi_broadcast_mode = KVM_SUPPRESS_EOI_BROADCAST_DISABLED;
> +
> r = 0;
> break;
> case KVM_CAP_X86_DISABLE_EXITS:

LGTM, will test this and reply on this thread.

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