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

From: Igor Mammedov
Date: Fri Dec 04 2015 - 06:25:57 EST


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

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