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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 2/5/18 3:53 pm, Balbir Singh wrote:
> On Wed,  2 May 2018 14:07:23 +1000
> Alexey Kardashevskiy <aik@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@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) {

This is harder to parse. My variant is bulky but straight forward otherwise.


> 
> 
> 
>>  			/*
>>  			 * 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?

Entry, page_shift come from the userspace and checked in appropriate
ioctl/hcall handlers.

> 
>> +	unsigned long subpg;
> 
> Why not just i?

I can imagine pages so huge so backing them with 4K will overflow 32bit
anyway. It is very (very) unlikely but it is 64bit arch anyway and there is
no much point in not-long types anyway.


>> +
>> +	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)
> 


-- 
Alexey