linux-kernel - Re: [PATCH 47/54] KVM: x86/mmu: Add helpers to do full reserved SPTE checks w/ generic MMU

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Date:   Wed, 23 Jun 2021 22:13:18 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH 47/54] KVM: x86/mmu: Add helpers to do full reserved SPTE
 checks w/ generic MMU

On 22/06/21 19:57, Sean Christopherson wrote:
> +	/*
> +	 * Use a bitwise-OR instead of a logical-OR to aggregate the reserved
> +	 * bits and EPT's invalid memtype/XWR checks to avoid an extra Jcc
> +	 * (this is used in hot paths).

Probably s/this is used in hot paths/this is extremely unlikely to be 
short-circuited as true/, since we are at it.

Paolo

> +	 */
> +	return __is_bad_mt_xwr(rsvd_check, spte) |
> +	       __is_rsvd_bits_set(rsvd_check, spte, level);