Subject: Re: [PATCH kernel v10 06/34] vfio: powerpc/spapr: Move page pinning from arch code to VFIO IOMMU driver

From: Alexey Kardashevskiy <[email-masked]>
Date: Wed, 13 May 2015 16:32:42 +1000

On 05/13/2015 03:58 PM, Gavin Shan wrote:
> On Tue, May 12, 2015 at 01:38:55AM +1000, Alexey Kardashevskiy wrote:
>> This moves page pinning (get_user_pages_fast()/put_page()) code out of
>> the platform IOMMU code and puts it to VFIO IOMMU driver where it belongs
>> to as the platform code does not deal with page pinning.
>>
>> This makes iommu_take_ownership()/iommu_release_ownership() deal with
>> the IOMMU table bitmap only.
>>
>> This removes page unpinning from iommu_take_ownership() as the actual
>> TCE table might contain garbage and doing put_page() on it is undefined
>> behaviour.
>>
>> Besides the last part, the rest of the patch is mechanical.
>>
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> [aw: for the vfio related changes]
>> Acked-by: Alex Williamson <[email-masked]>
>> Reviewed-by: David Gibson <[email-masked]>
>
> Reviewed-by: Gavin Shan <[email-masked]>
>
>> ---
>> Changes:
>> v9:
>> * added missing tce_iommu_clear call after iommu_release_ownership()
>> * brought @offset (a local variable) back to make patch even more
>> mechanical
>>
>> v4:
>> * s/iommu_tce_build(tbl, entry + 1/iommu_tce_build(tbl, entry + i/
>> ---
>> arch/powerpc/include/asm/iommu.h    |  4 --
>> arch/powerpc/kernel/iommu.c         | 55 -------------------------
>> drivers/vfio/vfio_iommu_spapr_tce.c | 80 +++++++++++++++++++++++++++++++------
>> 3 files changed, 67 insertions(+), 72 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
>> index 8353c86..e94a5e3 100644
>> --- a/arch/powerpc/include/asm/iommu.h
>> +++ b/arch/powerpc/include/asm/iommu.h
>> @@ -194,10 +194,6 @@ 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 int iommu_clear_tces_and_put_pages(struct iommu_table *tbl,
>> -		unsigned long entry, unsigned long pages);
>> -extern int iommu_put_tce_user_mode(struct iommu_table *tbl,
>> -		unsigned long entry, unsigned long tce);
>>
>> extern void iommu_flush_tce(struct iommu_table *tbl);
>> extern int iommu_take_ownership(struct iommu_table *tbl);
>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>> index 2c02d4c..8673c94 100644
>> --- a/arch/powerpc/kernel/iommu.c
>> +++ b/arch/powerpc/kernel/iommu.c
>> @@ -983,30 +983,6 @@ unsigned long iommu_clear_tce(struct iommu_table *tbl, unsigned long entry)
>> }
>> EXPORT_SYMBOL_GPL(iommu_clear_tce);
>>
>> -int iommu_clear_tces_and_put_pages(struct iommu_table *tbl,
>> -		unsigned long entry, unsigned long pages)
>> -{
>> -	unsigned long oldtce;
>> -	struct page *page;
>> -
>> -	for ( ; pages; --pages, ++entry) {
>> -		oldtce = iommu_clear_tce(tbl, entry);
>> -		if (!oldtce)
>> -			continue;
>> -
>> -		page = pfn_to_page(oldtce >> PAGE_SHIFT);
>> -		WARN_ON(!page);
>> -		if (page) {
>> -			if (oldtce & TCE_PCI_WRITE)
>> -				SetPageDirty(page);
>> -			put_page(page);
>> -		}
>> -	}
>> -
>> -	return 0;
>> -}
>> -EXPORT_SYMBOL_GPL(iommu_clear_tces_and_put_pages);
>> -
>> /*
>>   * hwaddr is a kernel virtual address here (0xc... bazillion),
>>   * tce_build converts it to a physical address.
>> @@ -1036,35 +1012,6 @@ int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
>> }
>> EXPORT_SYMBOL_GPL(iommu_tce_build);
>>
>> -int iommu_put_tce_user_mode(struct iommu_table *tbl, unsigned long entry,
>> -		unsigned long tce)
>> -{
>> -	int ret;
>> -	struct page *page = NULL;
>> -	unsigned long hwaddr, offset = tce & IOMMU_PAGE_MASK(tbl) & ~PAGE_MASK;
>> -	enum dma_data_direction direction = iommu_tce_direction(tce);
>> -
>> -	ret = get_user_pages_fast(tce & PAGE_MASK, 1,
>> -			direction != DMA_TO_DEVICE, &page);
>> -	if (unlikely(ret != 1)) {
>> -		/* pr_err("iommu_tce: get_user_pages_fast failed tce=%lx ioba=%lx ret=%d\n",
>> -				tce, entry << tbl->it_page_shift, ret); */
>> -		return -EFAULT;
>> -	}
>> -	hwaddr = (unsigned long) page_address(page) + offset;
>> -
>> -	ret = iommu_tce_build(tbl, entry, hwaddr, direction);
>> -	if (ret)
>> -		put_page(page);
>> -
>> -	if (ret < 0)
>> -		pr_err("iommu_tce: %s failed ioba=%lx, tce=%lx, ret=%d\n",
>> -			__func__, entry << tbl->it_page_shift, tce, ret);
>> -
>> -	return ret;
>> -}
>> -EXPORT_SYMBOL_GPL(iommu_put_tce_user_mode);
>> -
>> int iommu_take_ownership(struct iommu_table *tbl)
>> {
>> 	unsigned long sz = (tbl->it_size + 7) >> 3;
>> @@ -1078,7 +1025,6 @@ int iommu_take_ownership(struct iommu_table *tbl)
>> 	}
>>
>> 	memset(tbl->it_map, 0xff, sz);
>> -	iommu_clear_tces_and_put_pages(tbl, tbl->it_offset, tbl->it_size);
>>
>> 	/*
>> 	 * Disable iommu bypass, otherwise the user can DMA to all of
>> @@ -1096,7 +1042,6 @@ void iommu_release_ownership(struct iommu_table *tbl)
>> {
>> 	unsigned long sz = (tbl->it_size + 7) >> 3;
>>
>> -	iommu_clear_tces_and_put_pages(tbl, tbl->it_offset, tbl->it_size);
>> 	memset(tbl->it_map, 0, sz);
>>
>> 	/* Restore bit#0 set by iommu_init_table() */
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index 730b4ef..b95fa2b 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -147,6 +147,67 @@ static void tce_iommu_release(void *iommu_data)
>> 	kfree(container);
>> }
>>
>> +static int tce_iommu_clear(struct tce_container *container,
>> +		struct iommu_table *tbl,
>> +		unsigned long entry, unsigned long pages)
>> +{
>> +	unsigned long oldtce;
>> +	struct page *page;
>> +
>> +	for ( ; pages; --pages, ++entry) {
>> +		oldtce = iommu_clear_tce(tbl, entry);
>
> It might be nice to rename iommu_clear_tce() to iommu_tce_free() with another
> separate patch for two reasons as I can see: iommu_tce_{build, free} is one
> pair of functions doing opposite things. iommu_tce_free() is implemented based
> on ppc_md.tce_free() as iommu_tce_build() depends on ppc_md.tce_build().

Later in this patchset (in "[PATCH kernel v10 23/34] powerpc/iommu/powernv: 
Release replaced TCE") I am removing iommu_clear_tce() and 
iommu_tce_build() (there will be iommu_tce_xchg() only) so no point in 
renaming those.

-- 
Alexey