Re: [PATCH MANUALSEL 5.10 2/4] KVM: x86: Do not change ICR on write to APIC_SELF_IPI

[Paolo Bonzini]

On 4/27/22 17:54, Sasha Levin wrote:
> From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> [ Upstream commit d22a81b304a27fca6124174a8e842e826c193466 ]
>
> Emulating writes to SELF_IPI with a write to ICR has an unwanted side effect:
> the value of ICR in vAPIC page gets changed.  The lists SELF_IPI as write-only,
> with no associated MMIO offset, so any write should have no visible side
> effect in the vAPIC page.
>
> Reported-by: Chao Gao <chao.gao@xxxxxxxxx>
> Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>   arch/x86/kvm/lapic.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index de11149e28e0..e45ebf0870b6 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2106,10 +2106,9 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>   		break;
>   
>   	case APIC_SELF_IPI:
> -		if (apic_x2apic_mode(apic)) {
> -			kvm_lapic_reg_write(apic, APIC_ICR,
> -					    APIC_DEST_SELF | (val & APIC_VECTOR_MASK));
> -		} else
> +		if (apic_x2apic_mode(apic))
> +			kvm_apic_send_ipi(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK), 0);
> +		else
>   			ret = 1;
>   		break;
>   	default:

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>