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SubjectRe: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions
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On 15/01/2019 20:33, Gerald Schaefer wrote:
> On Tue, 15 Jan 2019 18:37:30 +0100
> Pierre Morel <pmorel@linux.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@linux.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@de.ibm.com>
>

Thanks.

Regards,
Pierre

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

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