linux-kernel - Re: [PATCH 01/23] KVM: MMU: pass uses_nx directly to reset_shadow_zero_bits

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Message-ID: <CALzav=c9GzV3To=tjU2sdCmkzh7WLK+i+W5pUjtfZsnkcg1dcQ@mail.gmail.com>
Date:   Mon, 7 Feb 2022 13:50:23 -0800
From:   David Matlack <dmatlack@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 01/23] KVM: MMU: pass uses_nx directly to reset_shadow_zero_bits_mask

On Mon, Feb 7, 2022 at 8:10 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Sat, Feb 05, 2022, Paolo Bonzini wrote:
> > On 2/4/22 18:59, David Matlack wrote:
> > > > + reset_shadow_zero_bits_mask(vcpu, context, is_efer_nx(context));
> > >
> > > Out of curiousity, how does KVM mitigate iTLB multi-hit when shadowing
> > > NPT and the guest has not enabled EFER.NX?
> >
> > You got me worried for a second but iTLB multihit is Intel-only, isn't it?
>
> AFAIK, yes, big Core only.  arch/x86/kernel/cpu/common.c sets NO_ITLB_MULTIHIT
> for all AMD, Hygon, and Atom CPUs.

Ah that's right, it's Intel-only. Thanks!