Re: [RFC PATCH 22/35] KVM: SVM: Add support for CR0 write traps for an SEV-ES guest

[Paolo Bonzini]

On 15/09/20 00:13, Sean Christopherson wrote:
> > +static void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0,
> > +			     unsigned long cr0)
> What about using __kvm_set_cr*() instead of kvm_post_set_cr*()?  That would
> show that __kvm_set_cr*() is a subordinate of kvm_set_cr*(), and from the
> SVM side would provide the hint that the code is skipping the front end of
> kvm_set_cr*().

No, kvm_post_set_cr0 is exactly the right name because it doesn't set 
any state.  __kvm_set_cr0 tells me that it is a (rarely used) way to set 
CR0, which this function isn't.

Sorry Tom for not catching this earlier.

Paolo

> > +{
> > +	unsigned long update_bits = X86_CR0_PG | X86_CR0_WP;
> > +
> > +	if ((cr0 ^ old_cr0) & X86_CR0_PG) {
> > +		kvm_clear_async_pf_completion_queue(vcpu);
> > +		kvm_async_pf_hash_reset(vcpu);
> > +	}
> > +
> > +	if ((cr0 ^ old_cr0) & update_bits)
> > +		kvm_mmu_reset_context(vcpu);
> > +
> > +	if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
> > +	    kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
> > +	    !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
> > +		kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
> > +}
> > +
> >   int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> >   {
> >   	unsigned long old_cr0 = kvm_read_cr0(vcpu);
> >   	unsigned long pdptr_bits = X86_CR0_CD | X86_CR0_NW | X86_CR0_PG;
> > -	unsigned long update_bits = X86_CR0_PG | X86_CR0_WP;
> >   
> >   	cr0 |= X86_CR0_ET;
> >   
> > @@ -842,22 +860,23 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> >   
> >   	kvm_x86_ops.set_cr0(vcpu, cr0);
> >   
> > -	if ((cr0 ^ old_cr0) & X86_CR0_PG) {
> > -		kvm_clear_async_pf_completion_queue(vcpu);
> > -		kvm_async_pf_hash_reset(vcpu);
> > -	}
> > +	kvm_post_set_cr0(vcpu, old_cr0, cr0);