On Wed, 2018-10-03 at 16:10 -0700, Alexander Duyck wrote:

quoted

-        * 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.