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

[Pierre Morel]

On 15/01/2019 20:33, Gerald Schaefer wrote:
> On Tue, 15 Jan 2019 18:37:30 +0100
> Pierre Morel <pmorel@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxx>

Thanks.

Regards,
Pierre

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