Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing

[Robin Murphy]

On 2021-06-24 07:05, Claire Chang wrote:
> On Thu, Jun 24, 2021 at 1:43 PM Christoph Hellwig <hch@xxxxxx> wrote:
> > On Wed, Jun 23, 2021 at 02:44:34PM -0400, Qian Cai wrote:
> > > is_swiotlb_force_bounce at /usr/src/linux-next/./include/linux/swiotlb.h:119
> > >
> > > is_swiotlb_force_bounce() was the new function introduced in this patch here.
> > >
> > > +static inline bool is_swiotlb_force_bounce(struct device *dev)
> > > +{
> > > +     return dev->dma_io_tlb_mem->force_bounce;
> > > +}
> >
> > To me the crash looks like dev->dma_io_tlb_mem is NULL.  Can you
> > turn this into :
> >
> >          return dev->dma_io_tlb_mem && dev->dma_io_tlb_mem->force_bounce;
> >
> > for a quick debug check?
>
> I just realized that dma_io_tlb_mem might be NULL like Christoph
> pointed out since swiotlb might not get initialized.
> However,  `Unable to handle kernel paging request at virtual address
> dfff80000000000e` looks more like the address is garbage rather than
> NULL?
> I wonder if that's because dev->dma_io_tlb_mem is not assigned
> properly (which means device_initialize is not called?).

What also looks odd is that the base "address" 0xdfff800000000000 is 
held in a couple of registers, but the offset 0xe looks too small to 
match up to any relevant structure member in that dereference chain :/

Robin.