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

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Message-ID: <YgFEVr9NM1vXdexg@google.com>
Date:   Mon, 7 Feb 2022 16:09:58 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     David Matlack <dmatlack@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, vkuznets@...hat.com
Subject: Re: [PATCH 01/23] KVM: MMU: pass uses_nx directly to
 reset_shadow_zero_bits_mask

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.