[RFC PATCH v3 21/59] KVM: x86: Add per-VM flag to disable in-kernel I/O APIC and level routes

isaku.yamahata
2021-11-25T00:21:44Z

From: Kai Huang <kai.huang@linux.intel.com>

Add a flag to let TDX disallow the in-kernel I/O APIC, level triggered
routes for a userspace I/O APIC, and anything else that relies on being
able to intercept EOIs. TDX-SEAM does not allow intercepting EOI.

Note, technically KVM could partially emulate the I/O APIC by allowing
only edge triggered interrupts, but that adds a lot of complexity for
basically zero benefit. Ideally KVM wouldn't even allow I/O APIC route
reservation, but disabling that is a train wreck for Qemu.

Signed-off-by: Kai Huang <kai.huang@linux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/ioapic.c | 4 ++++
arch/x86/kvm/irq_comm.c | 9 +++++++--
arch/x86/kvm/lapic.c | 3 ++-
arch/x86/kvm/x86.c | 6 ++++++
5 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f3808672c720..545b556e420c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1132,6 +1132,7 @@ struct kvm_arch {

enum kvm_irqchip_mode irqchip_mode;
u8 nr_reserved_ioapic_pins;
+ bool eoi_intercept_unsupported;

bool disabled_lapic_found;

diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 816a82515dcd..39a9031e11b1 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -311,6 +311,10 @@ void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm)
{
if (!ioapic_in_kernel(kvm))
return;
+
+ if (WARN_ON_ONCE(kvm->arch.eoi_intercept_unsupported))
+ return;
+
kvm_make_scan_ioapic_request(kvm);
}

diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index d5b72a08e566..bcfac99db579 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -123,7 +123,12 @@ EXPORT_SYMBOL_GPL(kvm_set_msi_irq);
static inline bool kvm_msi_route_invalid(struct kvm *kvm,
struct kvm_kernel_irq_routing_entry *e)
{
- return kvm->arch.x2apic_format && (e->msi.address_hi & 0xff);
+ struct msi_msg msg = { .address_lo = e->msi.address_lo,
+ .address_hi = e->msi.address_hi,
+ .data = e->msi.data };
+ return (kvm->arch.eoi_intercept_unsupported &&
+ msg.arch_data.is_level) ||
+ (kvm->arch.x2apic_format && (msg.address_hi & 0xff));
}

int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
@@ -385,7 +390,7 @@ int kvm_setup_empty_irq_routing(struct kvm *kvm)

void kvm_arch_post_irq_routing_update(struct kvm *kvm)
{
- if (!irqchip_split(kvm))
+ if (!irqchip_split(kvm) || kvm->arch.eoi_intercept_unsupported)
return;
kvm_make_scan_ioapic_request(kvm);
}
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 759952dd1222..1bfcd325d0d2 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -281,7 +281,8 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
if (old)
call_rcu(&old->rcu, kvm_apic_map_free);

- kvm_make_scan_ioapic_request(kvm);
+ if (!kvm->arch.eoi_intercept_unsupported)
+ kvm_make_scan_ioapic_request(kvm);
}

static inline void apic_set_spiv(struct kvm_lapic *apic, u32 val)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 535f65b0915d..1573dddd1e43 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6110,6 +6110,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
goto create_irqchip_unlock;

r = -EINVAL;
+ if (kvm->arch.eoi_intercept_unsupported)
+ goto create_irqchip_unlock;
+
if (kvm->created_vcpus)
goto create_irqchip_unlock;

@@ -6140,6 +6143,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
u.pit_config.flags = KVM_PIT_SPEAKER_DUMMY;
goto create_pit;
case KVM_CREATE_PIT2:
+ r = -EINVAL;
+ if (kvm->arch.eoi_intercept_unsupported)
+ goto out;
r = -EFAULT;
if (copy_from_user(&u.pit_config, argp,
sizeof(struct kvm_pit_config)))
--
2.25.1