[PATCH kernel 2/2] KVM: PPC: Allow backing bigger guest IOMMU pages with smaller physical pages

Balbir Singh bsingharora at gmail.com
Wed May 2 15:53:23 AEST 2018


On Wed,  2 May 2018 14:07:23 +1000
Alexey Kardashevskiy <aik at ozlabs.ru> wrote:

> At the moment we only support in the host the IOMMU page sizes which
> the guest is aware of, which is 4KB/64KB/16MB. However P9 does not support
> 16MB IOMMU pages, 2MB and 1GB pages are supported instead. We can still
> emulate bigger guest pages (for example 16MB) with smaller host pages
> (4KB/64KB/2MB).
> 
> This allows the physical IOMMU pages to use a page size smaller or equal
> than the guest visible IOMMU page size.
> 
> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
> ---
>  arch/powerpc/kvm/book3s_64_vio.c    | 66 +++++++++++++++++++++++++++++--------
>  arch/powerpc/kvm/book3s_64_vio_hv.c | 52 +++++++++++++++++++++++++----
>  2 files changed, 98 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index 041e54d..e10d6a3 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -176,14 +176,12 @@ extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
>  
>  		if (!tbltmp)
>  			continue;
> -		/*
> -		 * Make sure hardware table parameters are exactly the same;
> -		 * this is used in the TCE handlers where boundary checks
> -		 * use only the first attached table.
> -		 */
> -		if ((tbltmp->it_page_shift == stt->page_shift) &&
> -				(tbltmp->it_offset == stt->offset) &&
> -				(tbltmp->it_size == stt->size)) {
> +		/* Make sure hardware table parameters are compatible */
> +		if ((tbltmp->it_page_shift <= stt->page_shift) &&
> +				(tbltmp->it_offset << tbltmp->it_page_shift ==
> +				 stt->offset << stt->page_shift) &&
> +				(tbltmp->it_size << tbltmp->it_page_shift ==
> +				 stt->size << stt->page_shift)) {

Very difficult to parse

How about -

subpages_shift = (stt->page_shift - tbl->it_page_shift)

and then

matches_offset = !(tbltmp->it_offset - (stt->it_offset << subpages_shift));
matches_size = !(tbltmp->it_size - (stt->it_size << subpages_shift));

The condition then is just 

		if ((tbltmp->it_page_shift == stt->page_shift) &&
				matches_offset && matches_size) {



>  			/*
>  			 * Reference the table to avoid races with
>  			 * add/remove DMA windows.
> @@ -396,7 +394,7 @@ static long kvmppc_tce_iommu_mapped_dec(struct kvm *kvm,
>  	return H_SUCCESS;
>  }
>  
> -static long kvmppc_tce_iommu_unmap(struct kvm *kvm,
> +static long kvmppc_tce_iommu_do_unmap(struct kvm *kvm,
>  		struct iommu_table *tbl, unsigned long entry)
>  {
>  	enum dma_data_direction dir = DMA_NONE;
> @@ -416,7 +414,25 @@ static long kvmppc_tce_iommu_unmap(struct kvm *kvm,
>  	return ret;
>  }
>  
> -long kvmppc_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
> +static long kvmppc_tce_iommu_unmap(struct kvm *kvm,
> +		struct kvmppc_spapr_tce_table *stt, struct iommu_table *tbl,
> +		unsigned long entry)
> +{
> +	unsigned long ret = H_SUCCESS;
> +	unsigned long subpages = 1ULL << (stt->page_shift - tbl->it_page_shift);
> +	unsigned long io_entry = entry * subpages;

How do we know this multiplication does not overflow?

> +	unsigned long subpg;

Why not just i?

> +
> +	for (subpg = 0; subpg < subpages; ++subpg) {
> +		ret = kvmppc_tce_iommu_do_unmap(kvm, tbl, io_entry + subpg);
> +		if (ret != H_SUCCESS)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +
> +long kvmppc_tce_iommu_do_map(struct kvm *kvm, struct iommu_table *tbl,
>  		unsigned long entry, unsigned long ua,
>  		enum dma_data_direction dir)
>  {
> @@ -453,6 +469,28 @@ long kvmppc_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
>  	return 0;
>  }
>  
> +static long kvmppc_tce_iommu_map(struct kvm *kvm,
> +		struct kvmppc_spapr_tce_table *stt, struct iommu_table *tbl,
> +		unsigned long entry, unsigned long ua,
> +		enum dma_data_direction dir)
> +{
> +	unsigned long ret = H_SUCCESS;
> +	unsigned long subpages = 1ULL << (stt->page_shift - tbl->it_page_shift);
> +	unsigned long io_entry = entry * subpages;
> +	unsigned long subpg, pgoff;
> +
> +	for (subpg = 0, pgoff = 0; subpg < subpages;
> +			++subpg, pgoff += IOMMU_PAGE_SIZE(tbl)) {
> +
> +		ret = kvmppc_tce_iommu_do_map(kvm, tbl,
> +				io_entry + subpg, ua + pgoff, dir);
> +		if (ret != H_SUCCESS)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +
>  long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  		      unsigned long ioba, unsigned long tce)
>  {
> @@ -491,10 +529,10 @@ long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  
>  	list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>  		if (dir == DMA_NONE)
> -			ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
> +			ret = kvmppc_tce_iommu_unmap(vcpu->kvm, stt,
>  					stit->tbl, entry);
>  		else
> -			ret = kvmppc_tce_iommu_map(vcpu->kvm, stit->tbl,
> +			ret = kvmppc_tce_iommu_map(vcpu->kvm, stt, stit->tbl,
>  					entry, ua, dir);
>  
>  		if (ret == H_SUCCESS)
> @@ -570,7 +608,7 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>  			return H_PARAMETER;
>  
>  		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> -			ret = kvmppc_tce_iommu_map(vcpu->kvm,
> +			ret = kvmppc_tce_iommu_map(vcpu->kvm, stt,
>  					stit->tbl, entry + i, ua,
>  					iommu_tce_direction(tce));
>  
> @@ -618,7 +656,7 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
>  		unsigned long entry = ioba >> stt->page_shift;
>  
>  		for (i = 0; i < npages; ++i) {
> -			ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
> +			ret = kvmppc_tce_iommu_unmap(vcpu->kvm, stt,
>  					stit->tbl, entry + i);
>  
>  			if (ret == H_SUCCESS)
> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
> index e220fab..258e786 100644
> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> @@ -221,7 +221,7 @@ static long kvmppc_rm_tce_iommu_mapped_dec(struct kvm *kvm,
>  	return H_SUCCESS;
>  }
>  
> -static long kvmppc_rm_tce_iommu_unmap(struct kvm *kvm,
> +static long kvmppc_rm_tce_iommu_do_unmap(struct kvm *kvm,
>  		struct iommu_table *tbl, unsigned long entry)
>  {
>  	enum dma_data_direction dir = DMA_NONE;
> @@ -245,7 +245,25 @@ static long kvmppc_rm_tce_iommu_unmap(struct kvm *kvm,
>  	return ret;
>  }
>  
> -static long kvmppc_rm_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
> +static long kvmppc_rm_tce_iommu_unmap(struct kvm *kvm,
> +		struct kvmppc_spapr_tce_table *stt, struct iommu_table *tbl,
> +		unsigned long entry)
> +{
> +	unsigned long ret = H_SUCCESS;
> +	unsigned long subpages = 1ULL << (stt->page_shift - tbl->it_page_shift);
> +	unsigned long io_entry = entry * subpages;
> +	unsigned long subpg;
> +
> +	for (subpg = 0; subpg < subpages; ++subpg) {
> +		ret = kvmppc_rm_tce_iommu_do_unmap(kvm, tbl, io_entry + subpg);
> +		if (ret != H_SUCCESS)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +
> +static long kvmppc_rm_tce_iommu_do_map(struct kvm *kvm, struct iommu_table *tbl,
>  		unsigned long entry, unsigned long ua,
>  		enum dma_data_direction dir)
>  {
> @@ -290,6 +308,28 @@ static long kvmppc_rm_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
>  	return 0;
>  }
>  
> +static long kvmppc_rm_tce_iommu_map(struct kvm *kvm,
> +		struct kvmppc_spapr_tce_table *stt, struct iommu_table *tbl,
> +		unsigned long entry, unsigned long ua,
> +		enum dma_data_direction dir)
> +{
> +	unsigned long ret = H_SUCCESS;
> +	unsigned long subpages = 1ULL << (stt->page_shift - tbl->it_page_shift);
> +	unsigned long io_entry = entry * subpages;
> +	unsigned long subpg, pgoff;
> +
> +	for (subpg = 0, pgoff = 0; subpg < subpages;
> +			++subpg, pgoff += IOMMU_PAGE_SIZE(tbl)) {
> +
> +		ret = kvmppc_rm_tce_iommu_do_map(kvm, tbl,
> +				io_entry + subpg, ua + pgoff, dir);
> +		if (ret != H_SUCCESS)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +
>  long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  		unsigned long ioba, unsigned long tce)
>  {
> @@ -327,10 +367,10 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>  
>  	list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>  		if (dir == DMA_NONE)
> -			ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm,
> +			ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm, stt,
>  					stit->tbl, entry);
>  		else
> -			ret = kvmppc_rm_tce_iommu_map(vcpu->kvm,
> +			ret = kvmppc_rm_tce_iommu_map(vcpu->kvm, stt,
>  					stit->tbl, entry, ua, dir);
>  
>  		if (ret == H_SUCCESS)
> @@ -477,7 +517,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>  			return H_PARAMETER;
>  
>  		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> -			ret = kvmppc_rm_tce_iommu_map(vcpu->kvm,
> +			ret = kvmppc_rm_tce_iommu_map(vcpu->kvm, stt,
>  					stit->tbl, entry + i, ua,
>  					iommu_tce_direction(tce));
>  
> @@ -529,7 +569,7 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>  		unsigned long entry = ioba >> stt->page_shift;
>  
>  		for (i = 0; i < npages; ++i) {
> -			ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm,
> +			ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm, stt,
>  					stit->tbl, entry + i);
>  
>  			if (ret == H_SUCCESS)



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