linux-kernel - Re: [PATCH 04/12] KVM: MMU: WARN if PAE roots linger after kvm_mmu

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Message-ID: <YgWdyN3uarajuLdG@google.com>
Date:   Thu, 10 Feb 2022 23:20:40 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, mlevitsk@...hat.com, dmatlack@...gle.com
Subject: Re: [PATCH 04/12] KVM: MMU: WARN if PAE roots linger after
 kvm_mmu_unload

On Wed, Feb 09, 2022, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e0c0f0bc2e8b..7b5765ced928 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5065,12 +5065,21 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
>  	return r;
>  }
>  
> +static void __kvm_mmu_unload(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
> +{
> +	int i;
> +	kvm_mmu_free_roots(vcpu, mmu, KVM_MMU_ROOTS_ALL);
> +	WARN_ON(VALID_PAGE(mmu->root_hpa));
> +	if (mmu->pae_root) {
> +		for (i = 0; i < 4; ++i)
> +			WARN_ON(IS_VALID_PAE_ROOT(mmu->pae_root[i]));
> +	}

I'm somewhat ambivalent, but if you're at all on the fence, I vote to drop this
one.  I've always viewed the WARN on root_hpa as gratuitous.

But, if it helped during development, then why not...