linux-kernel - Re: [PATCH v11 033/113] KVM: x86/mmu: Track shadow MMIO value on a per-VM basis

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Date:   Mon, 27 Feb 2023 13:58:10 -0800
From:   Isaku Yamahata <isaku.yamahata@...il.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>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...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>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v11 033/113] KVM: x86/mmu: Track shadow MMIO value on a
 per-VM basis

On Mon, Jan 16, 2023 at 11:16:04AM +0000,
"Huang, Kai" <kai.huang@...el.com> wrote:

> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 6111e3e9266d..dffacb7eb15a 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -19,6 +19,14 @@ int kvm_mmu_init_tdp_mmu(struct kvm *kvm)
> >  {
> >  	struct workqueue_struct *wq;
> >  
> > +	/*
> > +	 * TDs require mmio_caching to clear suppress_ve bit of SPTE for GPA
> > +	 * of MMIO so that TD can convert #VE triggered by MMIO into
> > +	 * TDG.VP.VMCALL<MMIO>.
> > +	 */
> > +	if (kvm->arch.vm_type == KVM_X86_TDX_VM && !enable_mmio_caching)
> > +		return -EOPNOTSUPP;
> 
> SEV-ES does the check in hardware_setup:
> 
> void __init sev_hardware_setup(void)
> {
> 	...
> 	/*
>          * SEV-ES requires MMIO caching as KVM doesn't have access to the guest
>          * instruction stream, i.e. can't emulate in response to a #NPF and
>          * instead relies on #NPF(RSVD) being reflected into the guest as #VC
>          * (the guest can then do a #VMGEXIT to request MMIO emulation).
>          */
>         if (!enable_mmio_caching)
>                 goto out;
> 
> 	...
> }
> 
> TDX should be done in the same way.
> 
> And IMO this chunk really doesn't belong to this patch -- I interpret this patch
> as a "infrastructure patch to track shadow MMIO value on per-VM basis" (which
> even should have no functional change IMHO), but this chunk is clearly doing
> more than that.

It's cleaner to do in hardware_setup().  So I moved the logic into
hardware_setup() and an independent patch.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>