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SubjectRe: [PATCH v2 4/4] KVM: LAPIC: Don't silently accept bad vectors
2017-10-04 1:53 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
> 2017-09-28 18:04-0700, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>
>> Vectors 0-15 are reserved, and a physical LAPIC - upon sending or
>> receiving one - would generate an APIC error instead of doing the
>> requested action. Make our emulation behave similarly.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>> ---
>> arch/x86/kvm/lapic.c | 30 ++++++++++++++++++++++++++++--
>> 1 file changed, 28 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index 6bafd06..a779ba9 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -935,6 +935,25 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
>> return ret;
>> }
>>
>> +static void apic_error(struct kvm_lapic *apic, unsigned long errmask)
>> +{
>> + uint32_t esr;
>> +
>> + esr = kvm_lapic_get_reg(apic, APIC_ESR);
>> +
>> + if ((esr & errmask) != errmask) {
>
> The spec makes me think that there is going to be only 1 interrupt
> (regardless of the number errors) until the software writes 0 to
> APIC_ESR. Is there a better description than the following 10.5.3?
>
> The ESR is a write/read register. Before attempt to read from the ESR,
> software should first write to it. (The value written does not affect
> the values read subsequently; only zero may be written in x2APIC
> mode.) This write clears any previously logged errors and updates the
> ESR with any errors detected since the last write to the ESR. This
> write also rearms the APIC error interrupt triggering mechanism.
>
> This also describes a different handling of APIC_ESR -- APIC_ESR is
> updated only on software writes to APIC_ESR. All errors in between seem
> to be logged internally (not sure where to migrate it).

Is there any thing need to be changed in this function?

>
>> + uint32_t lvterr = kvm_lapic_get_reg(apic, APIC_LVTERR);
>> +
>> + kvm_lapic_set_reg(apic, APIC_ESR, esr | errmask);
>> + if (!(lvterr & APIC_LVT_MASKED)) {
>> + struct kvm_lapic_irq irq;
>> +
>> + irq.vector = lvterr & 0xff;
>> + kvm_irq_delivery_to_apic(apic->vcpu->kvm, apic, &irq, NULL);
>> + }
>> + }
>> +}
>> +
>> /*
>> * Add a pending IRQ into lapic.
>> * Return 1 if successfully added and 0 if discarded.
>> @@ -946,6 +965,11 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
>> int result = 0;
>> struct kvm_vcpu *vcpu = apic->vcpu;
>>
>> + if (unlikely(vector < 16) && delivery_mode == APIC_DM_FIXED) {
>> + apic_error(apic, APIC_ESR_RECVILL);
>
> The error is also triggered if lowest priority is supported and tries to
> deliver an invalid vector.

Could you point out this in SDM? :)

>
>> + return 0;
>> + }
>> +
>> trace_kvm_apic_accept_irq(vcpu->vcpu_id, delivery_mode,
>> trig_mode, vector);
>> switch (delivery_mode) {
>> @@ -1146,7 +1170,10 @@ static void apic_send_ipi(struct kvm_lapic *apic)
>> irq.trig_mode, irq.level, irq.dest_mode, irq.delivery_mode,
>> irq.vector, irq.msi_redir_hint);
>>
>> - kvm_irq_delivery_to_apic(apic->vcpu->kvm, apic, &irq, NULL);
>> + if (unlikely(irq.vector < 16 && irq.delivery_mode == APIC_DM_FIXED))
>
> Please check how APICv self-IPI acceleration behaves, so we're
> consistent.

There is no vmexit for APICv self-IPI, so I think we can't intercept the vector.

Regards,
Wanpeng Li

>
> Thanks.
>
>> + apic_error(apic, APIC_ESR_SENDILL);
>> + else
>> + kvm_irq_delivery_to_apic(apic->vcpu->kvm, apic, &irq, NULL);
>> }
>>
>> static u32 apic_get_tmcct(struct kvm_lapic *apic)
>> @@ -1734,7 +1761,6 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>> case APIC_LVTPC:
>> case APIC_LVT1:
>> case APIC_LVTERR:
>> - /* TODO: Check vector */
>> if (!kvm_apic_sw_enabled(apic))
>> val |= APIC_LVT_MASKED;
>>
>> --
>> 2.7.4
>>

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