linux-kernel - Re: [PATCH kernel v8 15/31] powerpc/iommu: Fix IOMMU ownership control functions

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Message-ID: <5530DD6D.8000001@ozlabs.ru>
Date:	Fri, 17 Apr 2015 20:16:13 +1000
From:	Alexey Kardashevskiy <aik@...abs.ru>
To:	David Gibson <david@...son.dropbear.id.au>
CC:	linuxppc-dev@...ts.ozlabs.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernel v8 15/31] powerpc/iommu: Fix IOMMU ownership control
 functions

On 04/16/2015 04:10 PM, David Gibson wrote:
> On Fri, Apr 10, 2015 at 04:30:57PM +1000, Alexey Kardashevskiy wrote:
>> This adds missing locks in iommu_take_ownership()/
>> iommu_release_ownership().
>>
>> This marks all pages busy in iommu_table::it_map in order to catch
>> errors if there is an attempt to use this table while ownership over it
>> is taken.
>>
>> This only clears TCE content if there is no page marked busy in it_map.
>> Clearing must be done outside of the table locks as iommu_clear_tce()
>> called from iommu_clear_tces_and_put_pages() does this.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
>> ---
>> Changes:
>> v5:
>> * do not store bit#0 value, it has to be set for zero-based table
>> anyway
>> * removed test_and_clear_bit
>> ---
>>   arch/powerpc/kernel/iommu.c | 26 ++++++++++++++++++++++----
>>   1 file changed, 22 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>> index 7d6089b..068fe4ff 100644
>> --- a/arch/powerpc/kernel/iommu.c
>> +++ b/arch/powerpc/kernel/iommu.c
>> @@ -1052,17 +1052,28 @@ EXPORT_SYMBOL_GPL(iommu_tce_build);
>>
>>   static int iommu_table_take_ownership(struct iommu_table *tbl)
>>   {
>> -	unsigned long sz = (tbl->it_size + 7) >> 3;
>> +	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>> +	int ret = 0;
>> +
>> +	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>> +	for (i = 0; i < tbl->nr_pools; i++)
>> +		spin_lock(&tbl->pools[i].lock);
>>
>>   	if (tbl->it_offset == 0)
>>   		clear_bit(0, tbl->it_map);
>>
>>   	if (!bitmap_empty(tbl->it_map, tbl->it_size)) {
>>   		pr_err("iommu_tce: it_map is not empty");
>> -		return -EBUSY;
>> +		ret = -EBUSY;
>> +		if (tbl->it_offset == 0)
>> +			set_bit(0, tbl->it_map);
>
> This really needs a comment.  Why on earth are you changing the it_map
> on a failure case?


Does this explain?

/*
  * The platform code reserves zero address in iommu_init_table().
  * As we cleared busy bit for page @0 before using bitmap_empty(),
  * we are restoring it now.
  */


>
>> +	} else {
>> +		memset(tbl->it_map, 0xff, sz);
>>   	}
>>
>> -	memset(tbl->it_map, 0xff, sz);
>> +	for (i = 0; i < tbl->nr_pools; i++)
>> +		spin_unlock(&tbl->pools[i].lock);
>> +	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
>>
>>   	return 0;
>>   }
>> @@ -1095,7 +1106,11 @@ EXPORT_SYMBOL_GPL(iommu_take_ownership);
>>
>>   static void iommu_table_release_ownership(struct iommu_table *tbl)
>>   {
>> -	unsigned long sz = (tbl->it_size + 7) >> 3;
>> +	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>> +
>> +	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>> +	for (i = 0; i < tbl->nr_pools; i++)
>> +		spin_lock(&tbl->pools[i].lock);
>>
>>   	memset(tbl->it_map, 0, sz);
>>
>> @@ -1103,6 +1118,9 @@ static void iommu_table_release_ownership(struct iommu_table *tbl)
>>   	if (tbl->it_offset == 0)
>>   		set_bit(0, tbl->it_map);
>>
>> +	for (i = 0; i < tbl->nr_pools; i++)
>> +		spin_unlock(&tbl->pools[i].lock);
>> +	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
>>   }
>>
>>   extern void iommu_release_ownership(struct iommu_table_group *table_group)
>


-- 
Alexey
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