Subject: Re: [PATCH kernel v8 17/31] powerpc/iommu/powernv: Release replaced TCE

From: Alexey Kardashevskiy <[email-masked]>
Date: Fri, 17 Apr 2015 20:37:54 +1000

On 04/16/2015 04:26 PM, David Gibson wrote:
> On Fri, Apr 10, 2015 at 04:30:59PM +1000, Alexey Kardashevskiy wrote:
>> At the moment writing new TCE value to the IOMMU table fails with EBUSY
>> if there is a valid entry already. However PAPR specification allows
>> the guest to write new TCE value without clearing it first.
>>
>> Another problem this patch is addressing is the use of pool locks for
>> external IOMMU users such as VFIO. The pool locks are to protect
>> DMA page allocator rather than entries and since the host kernel does
>> not control what pages are in use, there is no point in pool locks and
>> exchange()+put_page(oldtce) is sufficient to avoid possible races.
>>
>> This adds an exchange() callback to iommu_table_ops which does the same
>> thing as set() plus it returns replaced TCE and DMA direction so
>> the caller can release the pages afterwards.
>>
>> The returned old TCE value is a virtual address as the new TCE value.
>> This is different from tce_clear() which returns a physical address.
>>
>> This implements exchange() for P5IOC2/IODA/IODA2. This adds a requirement
>> for a platform to have exchange() implemented in order to support VFIO.
>>
>> This replaces iommu_tce_build() and iommu_clear_tce() with
>> a single iommu_tce_xchg().
>>
>> This makes sure that TCE permission bits are not set in TCE passed to
>> IOMMU API as those are to be calculated by platform code from DMA direction.
>>
>> This moves SetPageDirty() to the IOMMU code to make it work for both
>> VFIO ioctl interface in in-kernel TCE acceleration (when it becomes
>> available later).
>>
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> ---
>>   arch/powerpc/include/asm/iommu.h            | 17 ++++++--
>>   arch/powerpc/kernel/iommu.c                 | 53 +++++++++---------------
>>   arch/powerpc/platforms/powernv/pci-ioda.c   | 38 ++++++++++++++++++
>>   arch/powerpc/platforms/powernv/pci-p5ioc2.c |  3 ++
>>   arch/powerpc/platforms/powernv/pci.c        | 17 ++++++++
>>   arch/powerpc/platforms/powernv/pci.h        |  2 +
>>   drivers/vfio/vfio_iommu_spapr_tce.c         | 62 ++++++++++++++++++-----------
>>   7 files changed, 130 insertions(+), 62 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
>> index d1f8c6c..bde7ee7 100644
>> --- a/arch/powerpc/include/asm/iommu.h
>> +++ b/arch/powerpc/include/asm/iommu.h
>> @@ -44,11 +44,22 @@ extern int iommu_is_off;
>>   extern int iommu_force_on;
>>
>>   struct iommu_table_ops {
>> +	/* When called with direction==DMA_NONE, it is equal to clear() */
>>   	int (*set)(struct iommu_table *tbl,
>>   			long index, long npages,
>>   			unsigned long uaddr,
>>   			enum dma_data_direction direction,
>>   			struct dma_attrs *attrs);
>> +#ifdef CONFIG_IOMMU_API
>> +	/*
>> +	 * Exchanges existing TCE with new TCE plus direction bits;
>> +	 * returns old TCE and DMA direction mask
>> +	 */
>> +	int (*exchange)(struct iommu_table *tbl,
>> +			long index,
>> +			unsigned long *tce,
>> +			enum dma_data_direction *direction);
>> +#endif
>>   	void (*clear)(struct iommu_table *tbl,
>>   			long index, long npages);
>>   	unsigned long (*get)(struct iommu_table *tbl, long index);
>> @@ -152,6 +163,8 @@ extern void iommu_register_group(struct iommu_table_group *table_group,
>>   extern int iommu_add_device(struct device *dev);
>>   extern void iommu_del_device(struct device *dev);
>>   extern int __init tce_iommu_bus_notifier_init(void);
>> +extern long iommu_tce_xchg(struct iommu_table *tbl, unsigned long entry,
>> +		unsigned long *tce, enum dma_data_direction *direction);
>>   #else
>>   static inline void iommu_register_group(struct iommu_table_group *table_group,
>>   					int pci_domain_number,
>> @@ -231,10 +244,6 @@ extern int iommu_tce_clear_param_check(struct iommu_table *tbl,
>>   		unsigned long npages);
>>   extern int iommu_tce_put_param_check(struct iommu_table *tbl,
>>   		unsigned long ioba, unsigned long tce);
>> -extern int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
>> -		unsigned long hwaddr, enum dma_data_direction direction);
>> -extern unsigned long iommu_clear_tce(struct iommu_table *tbl,
>> -		unsigned long entry);
>>
>>   extern void iommu_flush_tce(struct iommu_table *tbl);
>>   extern int iommu_take_ownership(struct iommu_table_group *table_group);
>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>> index 068fe4ff..501e8ee 100644
>> --- a/arch/powerpc/kernel/iommu.c
>> +++ b/arch/powerpc/kernel/iommu.c
>> @@ -982,9 +982,6 @@ EXPORT_SYMBOL_GPL(iommu_tce_clear_param_check);
>>   int iommu_tce_put_param_check(struct iommu_table *tbl,
>>   		unsigned long ioba, unsigned long tce)
>>   {
>> -	if (!(tce & (TCE_PCI_WRITE | TCE_PCI_READ)))
>> -		return -EINVAL;
>> -
>>   	if (tce & ~(IOMMU_PAGE_MASK(tbl) | TCE_PCI_WRITE | TCE_PCI_READ))
>>   		return -EINVAL;
>>
>> @@ -1002,44 +999,20 @@ int iommu_tce_put_param_check(struct iommu_table *tbl,
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_tce_put_param_check);
>>
>> -unsigned long iommu_clear_tce(struct iommu_table *tbl, unsigned long entry)
>> -{
>> -	unsigned long oldtce;
>> -	struct iommu_pool *pool = get_pool(tbl, entry);
>> -
>> -	spin_lock(&(pool->lock));
>> -
>> -	oldtce = tbl->it_ops->get(tbl, entry);
>> -	if (oldtce & (TCE_PCI_WRITE | TCE_PCI_READ))
>> -		tbl->it_ops->clear(tbl, entry, 1);
>> -	else
>> -		oldtce = 0;
>> -
>> -	spin_unlock(&(pool->lock));
>> -
>> -	return oldtce;
>> -}
>> -EXPORT_SYMBOL_GPL(iommu_clear_tce);
>> -
>>   /*
>>    * hwaddr is a kernel virtual address here (0xc... bazillion),
>>    * tce_build converts it to a physical address.
>>    */
>> -int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
>> -		unsigned long hwaddr, enum dma_data_direction direction)
>> +long iommu_tce_xchg(struct iommu_table *tbl, unsigned long entry,
>> +		unsigned long *tce, enum dma_data_direction *direction)
>>   {
>> -	int ret = -EBUSY;
>> -	unsigned long oldtce;
>> -	struct iommu_pool *pool = get_pool(tbl, entry);
>> +	long ret;
>>
>> -	spin_lock(&(pool->lock));
>> +	ret = tbl->it_ops->exchange(tbl, entry, tce, direction);
>>
>> -	oldtce = tbl->it_ops->get(tbl, entry);
>> -	/* Add new entry if it is not busy */
>> -	if (!(oldtce & (TCE_PCI_WRITE | TCE_PCI_READ)))
>> -		ret = tbl->it_ops->set(tbl, entry, 1, hwaddr, direction, NULL);
>> -
>> -	spin_unlock(&(pool->lock));
>> +	if (!ret && ((*direction == DMA_FROM_DEVICE) ||
>> +			(*direction == DMA_BIDIRECTIONAL)))
>> +		SetPageDirty(pfn_to_page(__pa(*tce) >> PAGE_SHIFT));
>>
>>   	/* if (unlikely(ret))
>>   		pr_err("iommu_tce: %s failed on hwaddr=%lx ioba=%lx kva=%lx ret=%d\n",
>> @@ -1048,13 +1021,23 @@ int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
>>
>>   	return ret;
>>   }
>> -EXPORT_SYMBOL_GPL(iommu_tce_build);
>> +EXPORT_SYMBOL_GPL(iommu_tce_xchg);
>>
>>   static int iommu_table_take_ownership(struct iommu_table *tbl)
>>   {
>>   	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>>   	int ret = 0;
>>
>> +	/*
>> +	 * VFIO does not control TCE entries allocation and the guest
>> +	 * can write new TCEs on top of existing ones so iommu_tce_build()
>> +	 * must be able to release old pages. This functionality
>> +	 * requires exchange() callback defined so if it is not
>> +	 * implemented, we disallow taking ownership over the table.
>> +	 */
>> +	if (!tbl->it_ops->exchange)
>> +		return -EINVAL;
>> +
>>   	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>>   	for (i = 0; i < tbl->nr_pools; i++)
>>   		spin_lock(&tbl->pools[i].lock);
>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>> index fd993bc..4d80502 100644
>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>> @@ -1128,6 +1128,20 @@ static int pnv_ioda1_tce_build_vm(struct iommu_table *tbl, long index,
>>   	return ret;
>>   }
>>
>> +#ifdef CONFIG_IOMMU_API
>> +static int pnv_ioda1_tce_xchg_vm(struct iommu_table *tbl, long index,
>> +		unsigned long *tce, enum dma_data_direction *direction)
>> +{
>> +	long ret = pnv_tce_xchg(tbl, index, tce, direction);
>> +
>> +	if (!ret && (tbl->it_type &
>> +			(TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE)))
>> +		pnv_pci_ioda1_tce_invalidate(tbl, index, 1, false);
>> +
>> +	return ret;
>> +}
>> +#endif
>> +
>>   static void pnv_ioda1_tce_free_vm(struct iommu_table *tbl, long index,
>>   		long npages)
>>   {
>> @@ -1139,6 +1153,9 @@ static void pnv_ioda1_tce_free_vm(struct iommu_table *tbl, long index,
>>
>>   struct iommu_table_ops pnv_ioda1_iommu_ops = {
>>   	.set = pnv_ioda1_tce_build_vm,
>> +#ifdef CONFIG_IOMMU_API
>> +	.exchange = pnv_ioda1_tce_xchg_vm,
>> +#endif
>>   	.clear = pnv_ioda1_tce_free_vm,
>>   	.get = pnv_tce_get,
>>   };
>> @@ -1190,6 +1207,20 @@ static int pnv_ioda2_tce_build_vm(struct iommu_table *tbl, long index,
>>   	return ret;
>>   }
>>
>> +#ifdef CONFIG_IOMMU_API
>> +static int pnv_ioda2_tce_xchg_vm(struct iommu_table *tbl, long index,
>> +		unsigned long *tce, enum dma_data_direction *direction)
>> +{
>> +	long ret = pnv_tce_xchg(tbl, index, tce, direction);
>> +
>> +	if (!ret && (tbl->it_type &
>> +			(TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE)))
>> +		pnv_pci_ioda2_tce_invalidate(tbl, index, 1, false);
>> +
>> +	return ret;
>> +}
>> +#endif
>> +
>>   static void pnv_ioda2_tce_free_vm(struct iommu_table *tbl, long index,
>>   		long npages)
>>   {
>> @@ -1201,6 +1232,9 @@ static void pnv_ioda2_tce_free_vm(struct iommu_table *tbl, long index,
>>
>>   static struct iommu_table_ops pnv_ioda2_iommu_ops = {
>>   	.set = pnv_ioda2_tce_build_vm,
>> +#ifdef CONFIG_IOMMU_API
>> +	.exchange = pnv_ioda2_tce_xchg_vm,
>> +#endif
>>   	.clear = pnv_ioda2_tce_free_vm,
>>   	.get = pnv_tce_get,
>>   };
>> @@ -1353,6 +1387,7 @@ static void pnv_pci_ioda2_setup_bypass_pe(struct pnv_phb *phb,
>>   	pnv_pci_ioda2_set_bypass(pe, true);
>>   }
>>
>> +#ifdef CONFIG_IOMMU_API
>>   static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
>>   				     bool enable)
>>   {
>> @@ -1369,6 +1404,7 @@ static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
>>   static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
>>   	.set_ownership = pnv_ioda2_set_ownership,
>>   };
>> +#endif
>>
>>   static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
>>   				       struct pnv_ioda_pe *pe)
>> @@ -1437,7 +1473,9 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
>>   	}
>>   	tbl->it_ops = &pnv_ioda2_iommu_ops;
>>   	iommu_init_table(tbl, phb->hose->node);
>> +#ifdef CONFIG_IOMMU_API
>>   	pe->table_group.ops = &pnv_pci_ioda2_ops;
>> +#endif
>>   	iommu_register_group(&pe->table_group, phb->hose->global_number,
>>   			pe->pe_number);
>>
>> diff --git a/arch/powerpc/platforms/powernv/pci-p5ioc2.c b/arch/powerpc/platforms/powernv/pci-p5ioc2.c
>> index 6906a9c..d2d9092 100644
>> --- a/arch/powerpc/platforms/powernv/pci-p5ioc2.c
>> +++ b/arch/powerpc/platforms/powernv/pci-p5ioc2.c
>> @@ -85,6 +85,9 @@ static void pnv_pci_init_p5ioc2_msis(struct pnv_phb *phb) { }
>>
>>   static struct iommu_table_ops pnv_p5ioc2_iommu_ops = {
>>   	.set = pnv_tce_build,
>> +#ifdef CONFIG_IOMMU_API
>> +	.exchange = pnv_tce_xchg,
>> +#endif
>>   	.clear = pnv_tce_free,
>>   	.get = pnv_tce_get,
>>   };
>> diff --git a/arch/powerpc/platforms/powernv/pci.c b/arch/powerpc/platforms/powernv/pci.c
>> index a8c05de..a9797dd 100644
>> --- a/arch/powerpc/platforms/powernv/pci.c
>> +++ b/arch/powerpc/platforms/powernv/pci.c
>> @@ -615,6 +615,23 @@ int pnv_tce_build(struct iommu_table *tbl, long index, long npages,
>>   	return 0;
>>   }
>>
>> +#ifdef CONFIG_IOMMU_API
>> +int pnv_tce_xchg(struct iommu_table *tbl, long index,
>> +		unsigned long *tce, enum dma_data_direction *direction)
>> +{
>> +	u64 proto_tce = iommu_direction_to_tce_perm(*direction);
>> +	unsigned long newtce =  __pa(*tce) | proto_tce;
>> +	unsigned long idx = index - tbl->it_offset;
>> +
>> +	*tce = xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce));
>> +	*tce = (unsigned long) __va(be64_to_cpu(*tce));
>> +	*direction = iommu_tce_direction(*tce);
>> +	*tce &= ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +
>> +	return 0;
>> +}
>> +#endif
>> +
>>   void pnv_tce_free(struct iommu_table *tbl, long index, long npages)
>>   {
>>   	long i;
>> diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
>> index 0d4df32..4d1a78c 100644
>> --- a/arch/powerpc/platforms/powernv/pci.h
>> +++ b/arch/powerpc/platforms/powernv/pci.h
>> @@ -220,6 +220,8 @@ extern int pnv_tce_build(struct iommu_table *tbl, long index, long npages,
>>   		unsigned long uaddr, enum dma_data_direction direction,
>>   		struct dma_attrs *attrs);
>>   extern void pnv_tce_free(struct iommu_table *tbl, long index, long npages);
>> +extern int pnv_tce_xchg(struct iommu_table *tbl, long index,
>> +		unsigned long *tce, enum dma_data_direction *direction);
>>   extern unsigned long pnv_tce_get(struct iommu_table *tbl, long index);
>>   extern struct iommu_table_ops pnv_ioda1_iommu_ops;
>>
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index d5d8c50..7c3c215 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -251,9 +251,6 @@ static void tce_iommu_unuse_page(struct tce_container *container,
>>   {
>>   	struct page *page;
>>
>> -	if (!(oldtce & (TCE_PCI_READ | TCE_PCI_WRITE)))
>> -		return;
>> -
>>   	/*
>>   	 * VFIO cannot map/unmap when a container is not enabled so
>>   	 * we would not need this check but KVM could map/unmap and if
>> @@ -264,10 +261,6 @@ static void tce_iommu_unuse_page(struct tce_container *container,
>>   		return;
>>
>>   	page = pfn_to_page(__pa(oldtce) >> PAGE_SHIFT);
>> -
>> -	if (oldtce & TCE_PCI_WRITE)
>> -		SetPageDirty(page);
>> -
>
> Seems to me that unuse_page() should get a direction parameter,
> instead of moving the PageDirty (and DMA_NONE test) to all the
> callers.

Sorry, I am not following you here. There is just a single gateway for VFIO 
to the platform code which is iommu_tce_xchg() and this is where the 
SetPageDirty() check went. What are "all the callers"?

-- 
Alexey