linux-kernel - Re: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions

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Message-Id: <c7bd79f9-85f4-6fa7-8f4e-20eb3ed87d46@linux.ibm.com>
Date:   Wed, 16 Jan 2019 10:33:52 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:     joro@...tes.org, linux-s390@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        alex.williamson@...hat.com, shameerali.kolothum.thodi@...wei.com,
        walling@...ux.ibm.com
Subject: Re: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions

On 15/01/2019 20:33, Gerald Schaefer wrote:
> On Tue, 15 Jan 2019 18:37:30 +0100
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
>> The s390 iommu can only allow DMA transactions between the zPCI device
>> entries start_dma and end_dma.
>>
>> Let's declare the regions before start_dma and after end_dma as
>> reserved regions using the appropriate callback in iommu_ops.
>>
>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   drivers/iommu/s390-iommu.c | 29 +++++++++++++++++++++++++++++
>>   1 file changed, 29 insertions(+)
>>
>> diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
>> index 22d4db3..5ca91a1 100644
>> --- a/drivers/iommu/s390-iommu.c
>> +++ b/drivers/iommu/s390-iommu.c
>> @@ -363,6 +363,33 @@ void zpci_destroy_iommu(struct zpci_dev *zdev)
>>   	iommu_device_sysfs_remove(&zdev->iommu_dev);
>>   }
>>
>> +static void s390_get_resv_regions(struct device *dev, struct list_head *head)
>> +{
>> +	struct iommu_resv_region *region;
>> +	struct zpci_dev *zdev = to_pci_dev(dev)->sysdata;
>> +
>> +	region = iommu_alloc_resv_region(0, zdev->start_dma,
>> +					 0, IOMMU_RESV_RESERVED);
>> +	if (!region)
>> +		return;
>> +	list_add_tail(&region->list, head);
>> +
>> +	region = iommu_alloc_resv_region(zdev->end_dma + 1,
>> +					 ~0UL - zdev->end_dma,
>> +					 0, IOMMU_RESV_RESERVED);
> 
> Can you guarantee that start_dma will never be 0 and end_dma never ~0UL,
> even with future HW?
> 
> In any of these cases, your code would reserve strange ranges, and sysfs
> would report broken reserved ranges.
> 
> Maybe add a check for start_dma > 0 and end_dma < ULONG_MAX?

Yes, thanks.

> 
>> +	if (!region)
>> +		return;
>> +	list_add_tail(&region->list, head);
>> +}
>> +
>> +static void s390_put_resv_regions(struct device *dev, struct list_head *head)
>> +{
>> +	struct iommu_resv_region *entry, *next;
>> +
>> +	list_for_each_entry_safe(entry, next, head, list)
>> +		kfree(entry);
>> +}
> 
> It looks very wrong that there is no matching list_del() for the previous
> list_add_tail(). However, it seems to be done like this everywhere else,
> and the calling functions (currently) only use temporary list_heads as
> far as I can see, so I guess it should be OK (for now).
> 
> Still, a list_del() would be nice :-)

hum.
right.

> 
>> +
>>   static const struct iommu_ops s390_iommu_ops = {
>>   	.capable = s390_iommu_capable,
>>   	.domain_alloc = s390_domain_alloc,
>> @@ -376,6 +403,8 @@ static const struct iommu_ops s390_iommu_ops = {
>>   	.remove_device = s390_iommu_remove_device,
>>   	.device_group = generic_device_group,
>>   	.pgsize_bitmap = S390_IOMMU_PGSIZES,
>> +	.get_resv_regions = s390_get_resv_regions,
>> +	.put_resv_regions = s390_put_resv_regions,
>>   };
>>
>>   static int __init s390_iommu_init(void)
> 
> With the start/end_dma issue addressed (if necessary):
> Acked-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
> 

Thanks.

Regards,
Pierre

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany