Subject: Re: [PATCH kernel 4/9] powerpc/powernv/iommu: Add real mode version of xchg()

From: Alexey Kardashevskiy <[email-masked]>
Date: Mon, 7 Mar 2016 18:32:23 +1100

On 03/07/2016 05:05 PM, David Gibson wrote:
> On Mon, Mar 07, 2016 at 02:41:12PM +1100, Alexey Kardashevskiy wrote:
>> In real mode, TCE tables are invalidated using different
>> cache-inhibited store instructions which is different from
>> the virtual mode.
>>
>> This defines and implements exchange_rm() callback. This does not
>> define set_rm/clear_rm/flush_rm callbacks as there is no user for those -
>> exchange/exchange_rm are only to be used by KVM for VFIO.
>>
>> The exchange_rm callback is defined for IODA1/IODA2 powernv platforms.
>>
>> This replaces list_for_each_entry_rcu with its lockless version as
>> from now on pnv_pci_ioda2_tce_invalidate() can be called in
>> the real mode too.
>>
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> ---
>>   arch/powerpc/include/asm/iommu.h          |  7 +++++++
>>   arch/powerpc/kernel/iommu.c               | 15 +++++++++++++++
>>   arch/powerpc/platforms/powernv/pci-ioda.c | 28 +++++++++++++++++++++++++++-
>>   3 files changed, 49 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
>> index 7b87bab..3ca877a 100644
>> --- a/arch/powerpc/include/asm/iommu.h
>> +++ b/arch/powerpc/include/asm/iommu.h
>> @@ -64,6 +64,11 @@ struct iommu_table_ops {
>>   			long index,
>>   			unsigned long *hpa,
>>   			enum dma_data_direction *direction);
>> +	/* Real mode */
>> +	int (*exchange_rm)(struct iommu_table *tbl,
>> +			long index,
>> +			unsigned long *hpa,
>> +			enum dma_data_direction *direction);
>>   #endif
>>   	void (*clear)(struct iommu_table *tbl,
>>   			long index, long npages);
>> @@ -208,6 +213,8 @@ 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 *hpa, enum dma_data_direction *direction);
>> +extern long iommu_tce_xchg_rm(struct iommu_table *tbl, unsigned long entry,
>> +		unsigned long *hpa, enum dma_data_direction *direction);
>>   #else
>>   static inline void iommu_register_group(struct iommu_table_group *table_group,
>>   					int pci_domain_number,
>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>> index a8e3490..2fcc48b 100644
>> --- a/arch/powerpc/kernel/iommu.c
>> +++ b/arch/powerpc/kernel/iommu.c
>> @@ -1062,6 +1062,21 @@ void iommu_release_ownership(struct iommu_table *tbl)
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_release_ownership);
>>
>> +long iommu_tce_xchg_rm(struct iommu_table *tbl, unsigned long entry,
>> +		unsigned long *hpa, enum dma_data_direction *direction)
>> +{
>> +	long ret;
>> +
>> +	ret = tbl->it_ops->exchange_rm(tbl, entry, hpa, direction);
>> +
>> +	if (!ret && ((*direction == DMA_FROM_DEVICE) ||
>> +			(*direction == DMA_BIDIRECTIONAL)))
>> +		SetPageDirty(realmode_pfn_to_page(*hpa >> PAGE_SHIFT));
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_tce_xchg_rm);
>
>>   int iommu_add_device(struct device *dev)
>>   {
>>   	struct iommu_table *tbl;
>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>> index c5baaf3..bed1944 100644
>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>> @@ -1791,6 +1791,18 @@ static int pnv_ioda1_tce_xchg(struct iommu_table *tbl, long index,
>>
>>   	return ret;
>>   }
>> +
>> +static int pnv_ioda1_tce_xchg_rm(struct iommu_table *tbl, long index,
>> +		unsigned long *hpa, enum dma_data_direction *direction)
>> +{
>> +	long ret = pnv_tce_xchg(tbl, index, hpa, direction);
>> +
>> +	if (!ret && (tbl->it_type &
>> +			(TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE)))
>> +		pnv_pci_ioda1_tce_invalidate(tbl, index, 1, true);
>> +
>> +	return ret;
>> +}
>>   #endif
>
> Both your _rm variants are identical to the non _rm versions.  Why not
> just set the function poiinter to the same thing, rather than copying
> the whole function.

The last parameter - "rm" - to pnv_pci_ioda1_tce_invalidate() is different.

>
>>   static void pnv_ioda1_tce_free(struct iommu_table *tbl, long index,
>> @@ -1806,6 +1818,7 @@ static struct iommu_table_ops pnv_ioda1_iommu_ops = {
>>   	.set = pnv_ioda1_tce_build,
>>   #ifdef CONFIG_IOMMU_API
>>   	.exchange = pnv_ioda1_tce_xchg,
>> +	.exchange_rm = pnv_ioda1_tce_xchg_rm,
>>   #endif
>>   	.clear = pnv_ioda1_tce_free,
>>   	.get = pnv_tce_get,
>> @@ -1866,7 +1879,7 @@ static void pnv_pci_ioda2_tce_invalidate(struct iommu_table *tbl,
>>   {
>>   	struct iommu_table_group_link *tgl;
>>
>> -	list_for_each_entry_rcu(tgl, &tbl->it_group_list, next) {
>> +	list_for_each_entry_lockless(tgl, &tbl->it_group_list, next) {
>>   		struct pnv_ioda_pe *npe;
>>   		struct pnv_ioda_pe *pe = container_of(tgl->table_group,
>>   				struct pnv_ioda_pe, table_group);
>> @@ -1918,6 +1931,18 @@ static int pnv_ioda2_tce_xchg(struct iommu_table *tbl, long index,
>>
>>   	return ret;
>>   }
>> +
>> +static int pnv_ioda2_tce_xchg_rm(struct iommu_table *tbl, long index,
>> +		unsigned long *hpa, enum dma_data_direction *direction)
>> +{
>> +	long ret = pnv_tce_xchg(tbl, index, hpa, direction);
>> +
>> +	if (!ret && (tbl->it_type &
>> +			(TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE)))
>> +		pnv_pci_ioda2_tce_invalidate(tbl, index, 1, true);
>> +
>> +	return ret;
>> +}
>>   #endif
>>
>>   static void pnv_ioda2_tce_free(struct iommu_table *tbl, long index,
>> @@ -1939,6 +1964,7 @@ static struct iommu_table_ops pnv_ioda2_iommu_ops = {
>>   	.set = pnv_ioda2_tce_build,
>>   #ifdef CONFIG_IOMMU_API
>>   	.exchange = pnv_ioda2_tce_xchg,
>> +	.exchange_rm = pnv_ioda2_tce_xchg_rm,
>>   #endif
>>   	.clear = pnv_ioda2_tce_free,
>>   	.get = pnv_tce_get,
>

-- 
Alexey