Re: [PATCH V5 3/5] iommu/dma-iommu: Handle deferred devices

Tom Murphy
2019-08-17T07:20:08Z

On Sat, 17 Aug 2019 at 04:39, Hillf Danton <hdanton@sina.com> wrote:
>
>
> On Thu, 15 Aug 2019 12:09:41 +0100 Tom Murphy wrote:
> >
> > Handle devices which defer their attach to the iommu in the dma-iommu api
> >
> > Signed-off-by: Tom Murphy <murphyt7@tcd.ie>
> > ---
> > drivers/iommu/dma-iommu.c | 27 ++++++++++++++++++++++++++-
> > 1 file changed, 26 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index 2712fbc68b28..906b7fa14d3c 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -22,6 +22,7 @@
> > #include <linux/pci.h>
> > #include <linux/scatterlist.h>
> > #include <linux/vmalloc.h>
> > +#include <linux/crash_dump.h>
> >
> > struct iommu_dma_msi_page {
> > struct list_head list;
> > @@ -351,6 +352,21 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
> > return iova_reserve_iommu_regions(dev, domain);
> > }
> >
> > +static int handle_deferred_device(struct device *dev,
> > + struct iommu_domain *domain)
> > +{
> > + const struct iommu_ops *ops = domain->ops;
> > +
> > + if (!is_kdump_kernel())
> > + return 0;
> > +
> > + if (unlikely(ops->is_attach_deferred &&
> > + ops->is_attach_deferred(domain, dev)))
> > + return iommu_attach_device(domain, dev);
> > +
> > + return 0;
> > +}
> > +
> > /**
> > * dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
> > * page flags.
> > @@ -463,6 +479,9 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
> > size_t iova_off = iova_offset(iovad, phys);
> > dma_addr_t iova;
> >
> > + if (unlikely(handle_deferred_device(dev, domain)))
> > + return DMA_MAPPING_ERROR;
> > +
> > size = iova_align(iovad, size + iova_off);
> >
> > iova = iommu_dma_alloc_iova(domain, size, dma_get_mask(dev), dev);
>
> iommu_map_atomic() is applied to __iommu_dma_map() in 2/5.
> Is it an atomic context currently given the mutex_lock() in
> iommu_attach_device()?

I don't see your point here. __iommu_dma_map isn't called from
iommu_attach_device, why would we care about a mutex in
iommu_attach_device?

__iommu_dma_map can be called from an atomic context (it isn't always
but it does happen). __iommu_dma_map is called by iommu_dma_alloc
which implements the iommu_dma_ops::alloc function which by design
needs to be callable from an atomic context. Does that answer your
question?

>