linux-kernel - Re: [PATCH v3 34/37] KVM: nVMX: Don't flush TLB on nested VMX transition

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Date:   Tue, 24 Mar 2020 11:10:31 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.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, Ben Gardon <bgardon@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        John Haxby <john.haxby@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v3 34/37] KVM: nVMX: Don't flush TLB on nested VMX
 transition

On Tue, Mar 24, 2020 at 12:20:31PM +0100, Paolo Bonzini wrote:
> On 20/03/20 22:28, Sean Christopherson wrote:
> > Unconditionally skip the TLB flush triggered when reusing a root for a
> > nested transition as nested_vmx_transition_tlb_flush() ensures the TLB
> > is flushed when needed, regardless of whether the MMU can reuse a cached
> > root (or the last root).
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> So much for my WARN_ON. :)

Ha, yeah.  The double boolean also makes me nervous, but since there are
only two options, it seemed cleaner overall than a single mask-based param,
a ala EMULTYPE.