Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size

[Robin Murphy]

On 19/11/2018 14:18, Ramon Fried wrote:
> On Tue, Oct 9, 2018 at 8:02 AM Benjamin Herrenschmidt
> <benh@xxxxxxxxxxxxxxxxxxx> wrote:
> > On Wed, 2018-10-03 at 16:10 -0700, Alexander Duyck wrote:
> > > > -        * Because 32-bit DMA masks are so common we expect every architecture
> > > > -        * to be able to satisfy them - either by not supporting more physical
> > > > -        * memory, or by providing a ZONE_DMA32.  If neither is the case, the
> > > > -        * architecture needs to use an IOMMU instead of the direct mapping.
> > > > -        */
> > > > -       if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
> > > > +       u64 min_mask;
> > > > +
> > > > +       if (IS_ENABLED(CONFIG_ZONE_DMA))
> > > > +               min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
> > > > +       else
> > > > +               min_mask = DMA_BIT_MASK(32);
> > > > +
> > > > +       min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
> > > > +
> > > > +       if (mask >= phys_to_dma(dev, min_mask))
> > > >                   return 0;
> > > > -#endif
> > > >           return 1;
> > > >    }
> > >
> > > So I believe I have run into the same issue that Guenter reported. On
> > > an x86_64 system w/ Intel IOMMU. I wasn't able to complete boot and
> > > all probe attempts for various devices were failing with -EIO errors.
> > >
> > > I believe the last mask check should be "if (mask < phys_to_dma(dev,
> > > min_mask))" not a ">=" check.
> >
> > Right, that test is backwards. I needed to change it here too (powermac
> > with the rest of the powerpc series).
> >
> > Cheers,
> > Ben.
>
> Hi, I'm working on a MIPS64 soc with PCIe root complex on it, and it
> appears that this series of patches are causing all PCI drivers that
> request 64bit mask to fail with -5.
> It's broken in 4.19. However, I just checked, it working on master.
> We may need to backport a couple of patches to 4.19. I'm not sure
> though which patches should be backported as there were at least 10
> patches resolving this dma_direct area recently.
> Christoph, Robin.
> Can we ask Greg to backport all these changes ? What do you think ?

As far as I'm aware, the only real issue in 4.19 was my subtle breakage 
around setting bus_dma_mask - that's fixed by 6778be4e5209, which 
according to my inbox got picked up by autosel for 4.19 stable last week.

Robin.