Subject: Re: [PATCH kernel] KVM: PPC: Remove redundand permission bits removal

From: David Gibson <[email-masked]>
Date: Mon, 10 Sep 2018 14:50:18 +1000

On Thu, Sep 06, 2018 at 07:51:46PM +1000, Alexey Kardashevskiy wrote:
> The kvmppc_gpa_to_ua() helper itself takes care of the permission
> bits in the TCE and yet every single caller removes them.
> 
> This changes semantics of kvmppc_gpa_to_ua() so it takes TCEs
> (which are GPAs + TCE permission bits) to make the callers simpler.
> 
> This should cause no behavioural change.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>

Hmm.  I like shrinking the code, but it bothers me that a function
called simply kvmppc_gpa_to_ua() knows something about a TCE's
internal format.

I think either the TCE bit masking needs to happen in the callers, or
that function needs a name change.  Maybe kvmppc_tce_to_ua()?

> ---
> 
> This is not related to any bug, just noticed this while doing other things.
> 
> I can also rename kvmppc_gpa_to_ua() if it makes more sense, does not it?
> 
> ---
>  arch/powerpc/kvm/book3s_64_vio.c    | 10 +++-------
>  arch/powerpc/kvm/book3s_64_vio_hv.c | 16 ++++++----------
>  2 files changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index 174299d..7207481 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -378,8 +378,7 @@ static long kvmppc_tce_validate(struct kvmppc_spapr_tce_table *stt,
>  	if (iommu_tce_check_gpa(stt->page_shift, gpa))
>  		return H_TOO_HARD;
>  
> -	if (kvmppc_gpa_to_ua(stt->kvm, tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
> -				&ua, NULL))
> +	if (kvmppc_gpa_to_ua(stt->kvm, tce, &ua, NULL))
>  		return H_TOO_HARD;
>  
>  	list_for_each_entry_rcu(stit, &stt->iommu_tables, next) {
> @@ -553,8 +552,7 @@ long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  
>  	idx = srcu_read_lock(&vcpu->kvm->srcu);
>  
> -	if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm,
> -			tce & ~(TCE_PCI_READ | TCE_PCI_WRITE), &ua, NULL)) {
> +	if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm, tce, &ua, NULL)) {
>  		ret = H_PARAMETER;
>  		goto unlock_exit;
>  	}
> @@ -647,9 +645,7 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>  		}
>  		tce = be64_to_cpu(tce);
>  
> -		if (kvmppc_gpa_to_ua(vcpu->kvm,
> -				tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
> -				&ua, NULL))
> +		if (kvmppc_gpa_to_ua(vcpu->kvm, tce, &ua, NULL))
>  			return H_PARAMETER;
>  
>  		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
> index 5f810dc..a03cd93 100644
> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> @@ -110,8 +110,7 @@ static long kvmppc_rm_tce_validate(struct kvmppc_spapr_tce_table *stt,
>  	if (iommu_tce_check_gpa(stt->page_shift, gpa))
>  		return H_PARAMETER;
>  
> -	if (kvmppc_gpa_to_ua(stt->kvm, tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
> -				&ua, NULL))
> +	if (kvmppc_gpa_to_ua(stt->kvm, tce, &ua, NULL))
>  		return H_TOO_HARD;
>  
>  	list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> @@ -180,10 +179,10 @@ void kvmppc_tce_put(struct kvmppc_spapr_tce_table *stt,
>  }
>  EXPORT_SYMBOL_GPL(kvmppc_tce_put);
>  
> -long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
> +long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long tce,
>  		unsigned long *ua, unsigned long **prmap)
>  {
> -	unsigned long gfn = gpa >> PAGE_SHIFT;
> +	unsigned long gfn = tce >> PAGE_SHIFT;
>  	struct kvm_memory_slot *memslot;
>  
>  	memslot = search_memslots(kvm_memslots(kvm), gfn);
> @@ -191,7 +190,7 @@ long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
>  		return -EINVAL;
>  
>  	*ua = __gfn_to_hva_memslot(memslot, gfn) |
> -		(gpa & ~(PAGE_MASK | TCE_PCI_READ | TCE_PCI_WRITE));
> +		(tce & ~(PAGE_MASK | TCE_PCI_READ | TCE_PCI_WRITE));
>  
>  #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>  	if (prmap)
> @@ -366,8 +365,7 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  		return ret;
>  
>  	dir = iommu_tce_direction(tce);
> -	if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm,
> -			tce & ~(TCE_PCI_READ | TCE_PCI_WRITE), &ua, NULL))
> +	if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm, tce, &ua, NULL))
>  		return H_PARAMETER;
>  
>  	entry = ioba >> stt->page_shift;
> @@ -520,9 +518,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>  		unsigned long tce = be64_to_cpu(((u64 *)tces)[i]);
>  
>  		ua = 0;
> -		if (kvmppc_gpa_to_ua(vcpu->kvm,
> -				tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
> -				&ua, NULL))
> +		if (kvmppc_gpa_to_ua(vcpu->kvm, tce, &ua, NULL))
>  			return H_PARAMETER;
>  
>  		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson