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

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Date:   Tue, 20 Nov 2018 09:38:36 +0200
From:   Ramon Fried <ramon.fried@...il.com>
To:     robin.murphy@....com
Cc:     benh@...nel.crashing.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linuxppc-dev@...ts.ozlabs.org,
        open list <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, hch@....de, linux@...ck-us.net
Subject: Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size

On Mon, Nov 19, 2018 at 5:50 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 19/11/2018 14:18, Ramon Fried wrote:
> > On Tue, Oct 9, 2018 at 8:02 AM Benjamin Herrenschmidt
> > <benh@...nel.crashing.org> 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.
Yep, 6778be4e5209 fixes the issue.
Thanks a lot !
Ramon.