linux-kernel - Re: [PATCH v2 05/25] KVM: x86/mmu: rephrase unclear comment

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YieG2J+CdoUTTAB9@google.com>
Date:   Tue, 8 Mar 2022 16:39:52 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        dmatlack@...gle.com
Subject: Re: [PATCH v2 05/25] KVM: x86/mmu: rephrase unclear comment

On Mon, Feb 21, 2022, Paolo Bonzini wrote:
> If accessed bits are not supported there simple isn't any distinction
> between accessed and non-accessed gPTEs, so the comment does not make
> much sense.  Rephrase it in terms of what happens if accessed bits
> *are* supported.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 80b4b291002a..d1d17d28e81b 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -193,7 +193,7 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
>  	if (!FNAME(is_present_gpte)(gpte))
>  		goto no_present;
>  
> -	/* if accessed bit is not supported prefetch non accessed gpte */
> +	/* if accessed bit is supported, prefetch only accessed gpte */

Can we just reword the whole thing?  A/D bits being disabled is the anomaly,
leading with the "if" makes the logic we really care about seem like a secondary
concern.  E.g.

	/* Prefetch only accessed entries (unless A/D bits are disabled). */

>  	if (PT_HAVE_ACCESSED_DIRTY(vcpu->arch.mmu) &&
>  	    !(gpte & PT_GUEST_ACCESSED_MASK))
>  		goto no_present;
> -- 
> 2.31.1
> 
>