Subject: Re: [PATCH kernel v7 26/31] powerpc/iommu: Add userspace view of TCE table

From: Alexey Kardashevskiy <[email-masked]>
Date: Wed, 08 Apr 2015 13:22:00 +1000

On 04/03/2015 07:50 AM, Alex Williamson wrote:
>
> Should have sent this with the other comments, but found it hiding on my
> desktop...
>
> On Sat, 2015-03-28 at 01:55 +1100, Alexey Kardashevskiy wrote:
>> In order to support memory pre-registration, we need a way to track
>> the use of every registered memory region and only allow unregistration
>> if a region is not in use anymore. So we need a way to tell from what
>> region the just cleared TCE was from.
>>
>> This adds a userspace view of the TCE table into iommu_table struct.
>> It contains userspace address, one per TCE entry. The table is only
>> allocated when the ownership over an IOMMU group is taken which means
>> it is only used from outside of the powernv code (such as VFIO).
>>
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> ---
>>   arch/powerpc/include/asm/iommu.h          |  6 ++++++
>>   arch/powerpc/kernel/iommu.c               |  7 +++++++
>>   arch/powerpc/platforms/powernv/pci-ioda.c | 23 ++++++++++++++++++++++-
>>   3 files changed, 35 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
>> index 2c08c91..a768a4d 100644
>> --- a/arch/powerpc/include/asm/iommu.h
>> +++ b/arch/powerpc/include/asm/iommu.h
>> @@ -106,9 +106,15 @@ struct iommu_table {
>>   	unsigned long *it_map;       /* A simple allocation bitmap for now */
>>   	unsigned long  it_page_shift;/* table iommu page size */
>>   	struct iommu_table_group *it_group;
>> +	unsigned long *it_userspace; /* userspace view of the table */
>>   	struct iommu_table_ops *it_ops;
>>   };
>>
>> +#define IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry) \
>> +		((tbl)->it_userspace ? \
>> +			&((tbl)->it_userspace[(entry) - (tbl)->it_offset]) : \
>> +			NULL)
>> +
>>   /* Pure 2^n version of get_order */
>>   static inline __attribute_const__
>>   int get_iommu_order(unsigned long size, struct iommu_table *tbl)
>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>> index 0bcd988..82102d1 100644
>> --- a/arch/powerpc/kernel/iommu.c
>> +++ b/arch/powerpc/kernel/iommu.c
>> @@ -38,6 +38,7 @@
>>   #include <linux/pci.h>
>>   #include <linux/iommu.h>
>>   #include <linux/sched.h>
>> +#include <linux/vmalloc.h>
>>   #include <asm/io.h>
>>   #include <asm/prom.h>
>>   #include <asm/iommu.h>
>> @@ -1069,6 +1070,9 @@ static int iommu_table_take_ownership(struct iommu_table *tbl)
>>   		spin_unlock(&tbl->pools[i].lock);
>>   	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
>>
>> +	BUG_ON(tbl->it_userspace);
>> +	tbl->it_userspace = vzalloc(sizeof(*tbl->it_userspace) * tbl->it_size);
>> +
>
> -ENOMEM?
>
>>   	return 0;
>>   }
>>
>> @@ -1102,6 +1106,9 @@ static void iommu_table_release_ownership(struct iommu_table *tbl)
>>   {
>>   	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>>
>> +	vfree(tbl->it_userspace);
>> +	tbl->it_userspace = NULL;
>> +
>>   	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 bc36cf1..036f3c1 100644
>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>> @@ -26,6 +26,7 @@
>>   #include <linux/iommu.h>
>>   #include <linux/mmzone.h>
>>   #include <linux/sizes.h>
>> +#include <linux/vmalloc.h>
>>
>>   #include <asm/mmzone.h>
>>   #include <asm/sections.h>
>> @@ -1469,6 +1470,9 @@ static void pnv_pci_free_table(struct iommu_table *tbl)
>>   	if (!tbl->it_size)
>>   		return;
>>
>> +	if (tbl->it_userspace)
>
> Not necessary

Out of curiosity - why? Is every single implementation is known for 
checking the argument?

>
>> +		vfree(tbl->it_userspace);
>> +
>
> Why no NULL setting this time?

iommu_reset_table() (2 lines below) will do memset(0) on the entire struct.

>
>>   	pnv_free_tce_table(tbl->it_base, size, tbl->it_indirect_levels);
>>   	iommu_reset_table(tbl, "ioda2");
>>   }
>> @@ -1656,9 +1660,26 @@ static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
>>   	pnv_pci_ioda2_set_bypass(pe, !enable);
>>   }
>>
>> +static long pnv_pci_ioda2_create_table_with_uas(
>> +		struct iommu_table_group *table_group,
>> +		int num, __u32 page_shift, __u64 window_size, __u32 levels,
>> +		struct iommu_table *tbl)
>> +{
>> +	long ret = pnv_pci_ioda2_create_table(table_group, num,
>> +			page_shift, window_size, levels, tbl);
>> +
>> +	if (ret)
>> +		return ret;
>> +
>> +	BUG_ON(tbl->it_userspace);
>> +	tbl->it_userspace = vzalloc(sizeof(*tbl->it_userspace) * tbl->it_size);
>
> -ENOMEM
>
>> +
>> +	return 0;
>> +}
>> +
>>   static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
>>   	.set_ownership = pnv_ioda2_set_ownership,
>> -	.create_table = pnv_pci_ioda2_create_table,
>> +	.create_table = pnv_pci_ioda2_create_table_with_uas,
>>   	.set_window = pnv_pci_ioda2_set_window,
>>   	.unset_window = pnv_pci_ioda2_unset_window,
>>   };
>
>
>

Thanks for the review! What is overall resume? Another respin?

-- 
Alexey