linux-kernel - Re: [PATCH MANUALSEL 5.14 2/5] KVM: x86: WARN if APIC HW/SW disable static keys are non-zero on unload

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Date:   Tue, 26 Oct 2021 18:15:07 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH MANUALSEL 5.14 2/5] KVM: x86: WARN if APIC HW/SW disable
 static keys are non-zero on unload

On 25/10/21 22:38, Sasha Levin wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> [ Upstream commit 9139a7a64581c80d157027ae20e86f2f24d4292c ]
> 
> WARN if the static keys used to track if any vCPU has disabled its APIC
> are left elevated at module exit.  Unlike the underflow case, nothing in
> the static key infrastructure will complain if a key is left elevated,
> and because an elevated key only affects performance, nothing in KVM will
> fail if either key is improperly incremented.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Message-Id: <20211013003554.47705-3-seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>   arch/x86/kvm/lapic.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index ba5a27879f1d..18cb699b0a14 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2942,5 +2942,7 @@ int kvm_apic_accept_events(struct kvm_vcpu *vcpu)
>   void kvm_lapic_exit(void)
>   {
>   	static_key_deferred_flush(&apic_hw_disabled);
> +	WARN_ON(static_branch_unlikely(&apic_hw_disabled.key));
>   	static_key_deferred_flush(&apic_sw_disabled);
> +	WARN_ON(static_branch_unlikely(&apic_sw_disabled.key));
>   }
> 

NACK

Paolo