linux-kernel - Re: [PATCH] KVM: x86: Remove WARN sanity check on hypervisor timer vs. UNINITIALIZED vCPU

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Message-ID: <941e45b1-49eb-fcba-20d4-71b1db8041c5@redhat.com>
Date:   Thu, 10 Aug 2023 15:46:53 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yikebaer Aizezi <yikebaer61@...il.com>
Subject: Re: [PATCH] KVM: x86: Remove WARN sanity check on hypervisor timer
 vs. UNINITIALIZED vCPU

On 8/9/23 01:20, Sean Christopherson wrote:
>   		/*
> -		 * It should be impossible for the hypervisor timer to be in
> -		 * use before KVM has ever run the vCPU.
> +		 * Don't bother switching APIC timer emulation from the
> +		 * hypervisor timer to the software timer, the only way for the
> +		 * APIC timer to be active is if userspace stuffed vCPU state,
> +		 * i.e. put the vCPU into a nonsensical state.  Only an INIT
> +		 * will transition the vCPU out of UNINITIALIZED (without more
> +		 * state stuffing from userspace), which will reset the local
> +		 * APIC and thus smother the timer anyways, i.e. the APIC timer

"Cancel" is probably more understandable to non-native speakers, though 
undoubtedly less poetic.

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo

> +		 * IRQ(s) will be dropped no matter what.
>   		 */
> -		WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu));
> -