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Subject: Re: [PATCH 03/54] KVM: x86: Properly reset MMU context at vCPU
 RESET/INIT
To:     Sean Christopherson <seanjc@google.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Maxim Levitsky <mlevitsk@redhat.com>
References: <20210622175739.3610207-1-seanjc@google.com>
 <20210622175739.3610207-4-seanjc@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <2460a222-947a-6913-117c-f222f1dd0579@redhat.com>
Date:   Wed, 23 Jun 2021 15:59:50 +0200
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On 22/06/21 19:56, Sean Christopherson wrote:
> +	/*
> +	 * Reset the MMU context if paging was enabled prior to INIT (which is
> +	 * implied if CR0.PG=1 as CR0 will be '0' prior to RESET).  Unlike the
> +	 * standard CR0/CR4/EFER modification paths, only CR0.PG needs to be
> +	 * checked because it is unconditionally cleared on INIT and all other
> +	 * paging related bits are ignored if paging is disabled, i.e. CR0.WP,
> +	 * CR4, and EFER changes are all irrelevant if CR0.PG was '0'.
> +	 */
> +	if (old_cr0 & X86_CR0_PG)
> +		kvm_mmu_reset_context(vcpu);

Why not just check "if (init_event)", with a simple comment like

	/*
	 * Reset the MMU context in case paging was enabled prior to INIT (CR0
	 * will be '0' prior to RESET).
	 */

?

Paolo