Re: [PATCH v13 057/113] KVM: TDX: MTRR: implement get_mt_mask() for TDX

[Isaku Yamahata]

On Mon, Mar 27, 2023 at 09:54:40AM +0000,
"Huang, Kai" <kai.huang@xxxxxxxxx> wrote:

> > diff -u b/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > --- b/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -347,6 +347,25 @@
> >  	return 0;
> >  }
> >  
> > +u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> > +{
> > +	/* TDX private GPA is always WB. */
> > +	if (!(gfn & kvm_gfn_shared_mask(vcpu->kvm))) {
> 
> Are you still passing a "raw" GFN?  Could you explain why you choose this way?
> 
> > +		/* MMIO is only for shared GPA. */
> > +		WARN_ON_ONCE(is_mmio);
> > +		return  MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT;
> 
> I guess it's better to include VMX_EPT_IPAT_BIT bit.

On second thought, there is no need to check it.  We can simply drop this check.

u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
{
	if (is_mmio)
		return MTRR_TYPE_UNCACHABLE << VMX_EPT_MT_EPTE_SHIFT;

	if (!kvm_arch_has_noncoherent_dma(vcpu->kvm))
		return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT;

	/* TDX enforces CR0.CD = 0 and KVM MTRR emulation enforces writeback. */
	return MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT;
}

-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>