Subject: Re: [PATCH v3 04/18] vfio: powerpc: Move locked_vm accounting to a helper

From: Alexey Kardashevskiy <[email-masked]>
Date: Mon, 28 Jul 2014 19:12:07 +1000

On 07/28/2014 10:46 AM, Benjamin Herrenschmidt wrote:
> On Thu, 2014-07-24 at 18:47 +1000, Alexey Kardashevskiy wrote:
>> Additional DMA windows support is coming and accounting will include them
>> so let's move this code to a helper for reuse.
> 
> This code looks a LOT like the one you added in the previous patch
> (ie. kvmppc_account_memlimit()), though in a different place. I
> wonder if we should re-arrange things so that there is really
> only one version of it..

One copy is in VFIO driver, another in KVM, they meet in VFIO KVM device
(which may miss) or IOMMU code (drivers/iommu/iommu.c or
arch/powerpc/kernel/iommu.c) but this math has nothing to do with IOMMU. I
fail to see good common place for this.

> 
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> ---
>>  drivers/vfio/vfio_iommu_spapr_tce.c | 54 ++++++++++++++++++++++++-------------
>>  1 file changed, 36 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index a84788b..c8f7284 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -47,10 +47,40 @@ struct tce_container {
>>  	bool enabled;
>>  };
>>  
>> +/*
>> + * Checks ulimit in order not to let the user space to pin all
>> + * available memory for TCE tables.
>> + */
>> +static long tce_iommu_account_memlimit(struct iommu_table *tbl, bool inc)
>> +{
>> +	unsigned long ret = 0, locked, lock_limit;
>> +	long npages;
>> +
>> +	if (!current->mm)
>> +		return -ESRCH; /* process exited */
>> +
>> +	npages = (tbl->it_size << IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
>> +	if (!inc)
>> +		npages = -npages;
>> +
>> +	down_write(&current->mm->mmap_sem);
>> +	locked = current->mm->locked_vm + npages;
>> +	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>> +	if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
>> +		pr_warn("RLIMIT_MEMLOCK (%ld) exceeded\n",
>> +				rlimit(RLIMIT_MEMLOCK));
>> +		ret = -ENOMEM;
>> +	} else {
>> +		current->mm->locked_vm += npages;
>> +	}
>> +	up_write(&current->mm->mmap_sem);
>> +
>> +	return ret;
>> +}
>> +
>>  static int tce_iommu_enable(struct tce_container *container)
>>  {
>>  	int ret = 0;
>> -	unsigned long locked, lock_limit, npages;
>>  	struct iommu_table *tbl = container->tbl;
>>  
>>  	if (!container->tbl)
>> @@ -80,20 +110,11 @@ static int tce_iommu_enable(struct tce_container *container)
>>  	 * that would effectively kill the guest at random points, much better
>>  	 * enforcing the limit based on the max that the guest can map.
>>  	 */
>> -	down_write(&current->mm->mmap_sem);
>> -	npages = (tbl->it_size << IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
>> -	locked = current->mm->locked_vm + npages;
>> -	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>> -	if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
>> -		pr_warn("RLIMIT_MEMLOCK (%ld) exceeded\n",
>> -				rlimit(RLIMIT_MEMLOCK));
>> -		ret = -ENOMEM;
>> -	} else {
>> +	ret = tce_iommu_account_memlimit(tbl, true);
>> +	if (ret)
>> +		return ret;
>>  
>> -		current->mm->locked_vm += npages;
>> -		container->enabled = true;
>> -	}
>> -	up_write(&current->mm->mmap_sem);
>> +	container->enabled = true;
>>  
>>  	return ret;
>>  }
>> @@ -108,10 +129,7 @@ static void tce_iommu_disable(struct tce_container *container)
>>  	if (!container->tbl || !current->mm)
>>  		return;
>>  
>> -	down_write(&current->mm->mmap_sem);
>> -	current->mm->locked_vm -= (container->tbl->it_size <<
>> -			IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
>> -	up_write(&current->mm->mmap_sem);
>> +	tce_iommu_account_memlimit(container->tbl, false);
>>  }
>>  
>>  static void *tce_iommu_open(unsigned long arg)
> 
> 

-- 
Alexey