Re: [PATCH v3 5/8] iommu/vt-d: Implement def_domain_type iommu ops entry

Tom Murphy via iommu
2019-05-06T15:27:01Z

It looks like there is a bug in this code.

The behavior before this patch in __intel_map_single was that
iommu_no_mapping would call remove the attached si_domain for 32 bit
devices (in the dmar_remove_one_dev_info(dev) call in
iommu_no_mapping) and then allocate a new domain in
get_valid_domain_for_dev
old:
if (iommu_no_mapping(dev))
return paddr;
domain = get_valid_domain_for_dev(dev);
if (!domain)
return DMA_MAPPING_ERROR;

but in the new code we remove the attached si_domain but we WON'T
allocate a new domain and instead just return an error when we call
find_domain
new:
if (iommu_no_mapping(dev))
return paddr;

domain = find_domain(dev);
if (!domain)
return DMA_MAPPING_ERROR;

This is a bug, right?

On Tue, Apr 30, 2019 at 3:18 AM Lu Baolu <baolu.lu@linux.intel.com> wrote:
>
> Hi Christoph,
>
> On 4/30/19 4:03 AM, Christoph Hellwig wrote:
> >> @@ -3631,35 +3607,30 @@ static int iommu_no_mapping(struct device *dev)
> >> if (iommu_dummy(dev))
> >> return 1;
> >>
> >> - if (!iommu_identity_mapping)
> >> - return 0;
> >> -
> >
> > FYI, iommu_no_mapping has been refactored in for-next:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git/commit/?h=x86/vt-d&id=48b2c937ea37a3bece0094b46450ed5267525289
>
> Oh, yes! Thanks for letting me know this. Will rebase the code.
>
> >
> >> found = identity_mapping(dev);
> >> if (found) {
> >> + /*
> >> + * If the device's dma_mask is less than the system's memory
> >> + * size then this is not a candidate for identity mapping.
> >> + */
> >> + u64 dma_mask = *dev->dma_mask;
> >> +
> >> + if (dev->coherent_dma_mask &&
> >> + dev->coherent_dma_mask < dma_mask)
> >> + dma_mask = dev->coherent_dma_mask;
> >> +
> >> + if (dma_mask < dma_get_required_mask(dev)) {
> >
> > I know this is mostly existing code moved around, but it really needs
> > some fixing. For one dma_get_required_mask is supposed to return the
> > required to not bounce mask for the given device. E.g. for a device
> > behind an iommu it should always just return 32-bit. If you really
> > want to check vs system memory please call dma_direct_get_required_mask
> > without the dma_ops indirection.
> >
> > Second I don't even think we need to check the coherent_dma_mask,
> > dma_direct is pretty good at always finding memory even without
> > an iommu.
> >
> > Third this doesn't take take the bus_dma_mask into account.
> >
> > This probably should just be:
> >
> > if (min(*dev->dma_mask, dev->bus_dma_mask) <
> > dma_direct_get_required_mask(dev)) {
>
> Agreed and will add this in the next version.
>
> Best regards,
> Lu Baolu