[PATCH] KVM: x86: Fix virtual wire mode

[PATCH] KVM: x86: Fix virtual wire mode

[Jan H. Schönherr]

Intel SDM says, that at most one LAPIC should be configured with ExtINT
delivery. KVM configures all LAPICs this way. This causes pic_unlock()
to kick the first available vCPU from the internal KVM data structures.
If this vCPU is not the BSP, but some not-yet-booted AP, the BSP may
never realize that there is an interrupt.

Fix that by enabling ExtINT delivery only for the BSP.

This allows booting a Linux guest without a TSC in the above situation.
Otherwise the BSP gets stuck in calibrate_delay_converge().

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
---
 arch/x86/kvm/lapic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index c329d28..df1b865 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1934,7 +1934,8 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 	for (i = 0; i < KVM_APIC_LVT_NUM; i++)
 		kvm_lapic_set_reg(apic, APIC_LVTT + 0x10 * i, APIC_LVT_MASKED);
 	apic_update_lvtt(apic);
-	if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_LINT0_REENABLED))
+	if (kvm_vcpu_is_reset_bsp(vcpu) &&
+	    kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_LINT0_REENABLED))
 		kvm_lapic_set_reg(apic, APIC_LVT0,
 			     SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT));
 	apic_manage_nmi_watchdog(apic, kvm_lapic_get_reg(apic, APIC_LVT0));
-- 
2.3.1.dirty

Re: [PATCH] KVM: x86: Fix virtual wire mode

[Wanpeng Li]

2017-05-20 19:24 GMT+08:00 Jan H. Schönherr <jschoenh@amazon.de>:
> Intel SDM says, that at most one LAPIC should be configured with ExtINT
> delivery. KVM configures all LAPICs this way. This causes pic_unlock()
> to kick the first available vCPU from the internal KVM data structures.
> If this vCPU is not the BSP, but some not-yet-booted AP, the BSP may
> never realize that there is an interrupt.
>
> Fix that by enabling ExtINT delivery only for the BSP.
>
> This allows booting a Linux guest without a TSC in the above situation.
> Otherwise the BSP gets stuck in calibrate_delay_converge().
>
> Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>

Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>

> ---
>  arch/x86/kvm/lapic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index c329d28..df1b865 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1934,7 +1934,8 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
>         for (i = 0; i < KVM_APIC_LVT_NUM; i++)
>                 kvm_lapic_set_reg(apic, APIC_LVTT + 0x10 * i, APIC_LVT_MASKED);
>         apic_update_lvtt(apic);
> -       if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_LINT0_REENABLED))
> +       if (kvm_vcpu_is_reset_bsp(vcpu) &&
> +           kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_LINT0_REENABLED))
>                 kvm_lapic_set_reg(apic, APIC_LVT0,
>                              SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT));
>         apic_manage_nmi_watchdog(apic, kvm_lapic_get_reg(apic, APIC_LVT0));
> --
> 2.3.1.dirty
>

Re: [PATCH] KVM: x86: Fix virtual wire mode

[Jan H. Schönherr]

On 05/22/2017 09:19 AM, Xiao Guangrong wrote:
>
>
> On 05/20/2017 07:24 PM, Jan H. Schönherr wrote:
>> Intel SDM says, that at most one LAPIC should be configured with ExtINT
>> delivery. KVM configures all LAPICs this way. This causes pic_unlock()
>> to kick the first available vCPU from the internal KVM data structures.
>> If this vCPU is not the BSP, but some not-yet-booted AP, the BSP may
>> never realize that there is an interrupt.
>>
>> Fix that by enabling ExtINT delivery only for the BSP.
>>
>> This allows booting a Linux guest without a TSC in the above situation.
>> Otherwise the BSP gets stuck in calibrate_delay_converge().
>
> Patch looks good to me.
>
> BTW, what benefit do you want to get from notsc?
>

None. I just want my guest to boot in case it does that. :)

Regards
Jan
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B