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KVM: x86: WARN if KVM emulates an IPI without clearing the BUSY flag

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WARN if KVM emulates an IPI without clearing the BUSY flag, failure to do
so could hang the guest if it waits for the IPI be sent.

Opportunistically use APIC_ICR_BUSY macro instead of open coding the
magic number, and add a comment to clarify why kvm_recalculate_apic_map()
is unconditionally invoked (it's really, really confusing for IPIs due to
the existence of fast paths that don't trigger a potential recalc).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220204214205.3306634-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-02-04 21:42:00 +00:00 committed by Paolo Bonzini
parent b51818afdc
commit bd17f417c0
2 changed files with 13 additions and 6 deletions
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10
arch/x86/kvm/lapic.c
View File

@ -1275,6 +1275,9 @@ void kvm_apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
{
struct kvm_lapic_irq irq;
/* KVM has no delay and should always clear the BUSY/PENDING flag. */
WARN_ON_ONCE(icr_low & APIC_ICR_BUSY);
irq.vector = icr_low & APIC_VECTOR_MASK;
irq.delivery_mode = icr_low & APIC_MODE_MASK;
irq.dest_mode = icr_low & APIC_DEST_MASK;
@ -2053,7 +2056,7 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
}
case APIC_ICR:
/* No delay here, so we always clear the pending bit */
val &= ~(1 << 12);
val &= ~APIC_ICR_BUSY;
kvm_apic_send_ipi(apic, val, kvm_lapic_get_reg(apic, APIC_ICR2));
kvm_lapic_set_reg(apic, APIC_ICR, val);
break;
@ -2131,6 +2134,11 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
break;
}
/*
* Recalculate APIC maps if necessary, e.g. if the software enable bit
* was toggled, the APIC ID changed, etc... The maps are marked dirty
* on relevant changes, i.e. this is a nop for most writes.
*/
kvm_recalculate_apic_map(apic->vcpu->kvm);
return ret;

9
arch/x86/kvm/x86.c
View File

@ -2039,11 +2039,10 @@ static int handle_fastpath_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u64 data
return 1;
if (((data & APIC_SHORT_MASK) == APIC_DEST_NOSHORT) &&
((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) &&
((data & APIC_MODE_MASK) == APIC_DM_FIXED) &&
((u32)(data >> 32) != X2APIC_BROADCAST)) {
data &= ~(1 << 12);
((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) &&
((data & APIC_MODE_MASK) == APIC_DM_FIXED) &&
((u32)(data >> 32) != X2APIC_BROADCAST)) {
data &= ~APIC_ICR_BUSY;
kvm_apic_send_ipi(vcpu->arch.apic, (u32)data, (u32)(data >> 32));
kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR2, (u32)(data >> 32));
kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR, (u32)data);