linux-kernel - Re: [PATCH v11 055/113] KVM: x86/VMX: introduce vmx tlb_remote_flush and tlb_remote_flush_with

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Message-ID: <Y8bSpdplnlRus3lx@google.com>
Date:   Tue, 17 Jan 2023 16:53:57 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>
Subject: Re: [PATCH v11 055/113] KVM: x86/VMX: introduce vmx tlb_remote_flush
 and tlb_remote_flush_with_range

On Tue, Jan 17, 2023, Huang, Kai wrote:
> On Thu, 2023-01-12 at 08:32 -0800, isaku.yamahata@...el.com wrote:
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -244,7 +244,7 @@ static void kvm_flush_remote_tlbs_with_range(struct kvm *kvm,
> >  {
> >  	int ret = -ENOTSUPP;
> >  
> > -	if (range && kvm_x86_ops.tlb_remote_flush_with_range)
> > +	if (range && kvm_available_flush_tlb_with_range())
> >  		ret = static_call(kvm_x86_tlb_remote_flush_with_range)(kvm, range);
> 
> Again, IMHO this code change doesn't make code any clearer.  With the new code,
> I need to go into the kvm_available_flush_tlb_with_range() to see what's going
> on, but with the old code I don't.

Agreed.  Though I think this patch as a whole can be replaced with a more
straightforward solution.

hv_remote_flush_tlb() is used when KVM is running as a Hyper-V guest, whereas
TDX requires running KVM on bare metal.  KVM should simply disallow TDX when a
hypervisor is detected, then there's no need for vmx_tlb_remote_flush_with_range().