2015-05-22 17:22:19

by Radim Krčmář

Subject: [PATCH] KVM: x86: preserve x2APIC LDR on INIT

Logical x2APIC stops working if we rewrite it with zeros.
The best references are SDM April 2015: 10.12.10.1 Logical Destination
Mode in x2APIC Mode

[...], the LDR are initialized by hardware based on the value of
x2APIC ID upon x2APIC state transitions.

and SDM April 2015: 10.12.10.2 Deriving Logical x2APIC ID from the Local
x2APIC ID

The LDR initialization occurs whenever the x2APIC mode is enabled

Signed-off-by: Radim Krčmář <[email protected]>
---
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 c2a7d8a7a414..c789e00dfa8b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1594,7 +1594,8 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
apic_set_reg(apic, APIC_DFR, 0xffffffffU);
apic_set_spiv(apic, 0xff);
apic_set_reg(apic, APIC_TASKPRI, 0);
- kvm_apic_set_ldr(apic, 0);
+ if (!apic_x2apic_mode(apic))
+ kvm_apic_set_ldr(apic, 0);
apic_set_reg(apic, APIC_ESR, 0);
apic_set_reg(apic, APIC_ICR, 0);
apic_set_reg(apic, APIC_ICR2, 0);
--
2.4.1

2015-05-26 13:29:41

by Paolo Bonzini

Subject: Re: [PATCH] KVM: x86: preserve x2APIC LDR on INIT

On 22/05/2015 19:22, Radim Krčmář wrote:
> Logical x2APIC stops working if we rewrite it with zeros.
> The best references are SDM April 2015: 10.12.10.1 Logical Destination
> Mode in x2APIC Mode
>
> [...], the LDR are initialized by hardware based on the value of
> x2APIC ID upon x2APIC state transitions.
>
> and SDM April 2015: 10.12.10.2 Deriving Logical x2APIC ID from the Local
> x2APIC ID
>
> The LDR initialization occurs whenever the x2APIC mode is enabled
>
> Signed-off-by: Radim Krčmář <[email protected]>
> ---
> 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 c2a7d8a7a414..c789e00dfa8b 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1594,7 +1594,8 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
> apic_set_reg(apic, APIC_DFR, 0xffffffffU);
> apic_set_spiv(apic, 0xff);
> apic_set_reg(apic, APIC_TASKPRI, 0);
> - kvm_apic_set_ldr(apic, 0);
> + if (!apic_x2apic_mode(apic))
> + kvm_apic_set_ldr(apic, 0);
> apic_set_reg(apic, APIC_ESR, 0);
> apic_set_reg(apic, APIC_ICR, 0);
> apic_set_reg(apic, APIC_ICR2, 0);
>

Applied, thanks.

Paolo