linux-kernel - Re: [PATCH v4 18/32] KVM: x86: Explicitly skip optimized logical map setup if vCPU's LDR==0

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Message-ID: <e3e9da038f9ea83b1dc81e2532a737e98b2f2195.camel@redhat.com>
Date:   Thu, 08 Dec 2022 23:56:51 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Li RongQing <lirongqing@...du.com>
Subject: Re: [PATCH v4 18/32] KVM: x86: Explicitly skip optimized logical
 map setup if vCPU's LDR==0

On Sat, 2022-10-01 at 00:59 +0000, Sean Christopherson wrote:
> Explicitly skip the optimized map setup if the vCPU's LDR is '0', i.e. if
> the vCPU will never respond to logical mode interrupts.  KVM already
> skips setup in this case, but relies on kvm_apic_map_get_logical_dest()
> to generate mask==0.  KVM still needs the mask=0 check as a non-zero LDR
> can yield mask==0 depending on the mode, but explicitly handling the LDR
> will make it simpler to clean up the logical mode tracking in the future.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/lapic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 42b61469674d..cef8b202490b 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -286,10 +286,12 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
>  			continue;
>  
>  		ldr = kvm_lapic_get_reg(apic, APIC_LDR);
> +		if (!ldr)
> +			continue;
>  
>  		if (apic_x2apic_mode(apic)) {
>  			new->mode |= KVM_APIC_MODE_X2APIC;
> -		} else if (ldr) {
> +		} else {
>  			ldr = GET_APIC_LOGICAL_ID(ldr);
>  			if (kvm_lapic_get_reg(apic, APIC_DFR) == APIC_DFR_FLAT)
>  				new->mode |= KVM_APIC_MODE_XAPIC_FLAT;

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky