[PATCH v2 0/2] x86: enable SWIOTLB if system has SRAT memory regions above MAX_DMA32_PFN

[Igor Mammedov <imammedo@redhat.com>]

changes since v1:
  - reduce # of #ifdefs by introducing max_possible_pfn
    global variable
  - don't check 'acpi_no_memhotplug=1' for disabling
    SWIOTLB initialization, since existing 'no_iommu'
    kernel option could be used to the same effect.
  - split into 2 patches
      - 1st adds max_possible_pfn,
      - 2nd fixes bug enabling SWIOTLB when it's needed

when memory hotplug enabled system is booted with less
than 4GB of RAM and then later more RAM is hotplugged
32-bit devices stop functioning with following error:

 nommu_map_single: overflow 327b4f8c0+1522 of device mask ffffffff

the reason for this is that if x86_64 system were booted
with RAM less than 4GB, it doesn't enable SWIOTLB and
when memory is hotplugged beyond MAX_DMA32_PFN, devices
that expect 32-bit addresses can't handle 64-bit addresses.

Fix it by tracking max possible PFN when parsing
memory affinity structures from SRAT ACPI table and
enable SWIOTLB if there is hotpluggable memory
regions beyond MAX_DMA32_PFN.

It fixes KVM guests when they use emulated devices
(reproduces with ata_piix, e1000 and usb devices,
 RHBZ: 1275941, 1275977, 1271527)
It also fixes the HyperV, VMWare with emulated devices
which are affected by this issue as well.

ref to v1:
  https://lkml.org/lkml/2015/11/30/594

Igor Mammedov (2):
  x86: introduce max_possible_pfn
  x86_64: enable SWIOTLB if system has SRAT memory regions above
    MAX_DMA32_PFN

 arch/x86/kernel/pci-swiotlb.c | 2 +-
 arch/x86/kernel/setup.c       | 2 ++
 arch/x86/mm/srat.c            | 3 +++
 include/linux/bootmem.h       | 4 ++++
 mm/bootmem.c                  | 1 +
 mm/nobootmem.c                | 1 +
 6 files changed, 12 insertions(+), 1 deletion(-)

-- 
1.8.3.1