linux-kernel - Re: [PATCH] KVM: x86: preserve x2APIC LDR on INIT

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Message-ID: <55644D12.6020301@redhat.com>
Date:	Tue, 26 May 2015 12:38:10 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	linux-kernel@...r.kernel.org
CC:	kvm@...r.kernel.org
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 <rkrcmar@...hat.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 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
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