[PATCH v2 2/2] x86_64: enable SWIOTLB if system has SRAT memory regions above MAX_DMA32_PFN

[Igor Mammedov <imammedo@redhat.com>]

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.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 arch/x86/kernel/pci-swiotlb.c | 2 +-
 arch/x86/mm/srat.c            | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index adf0392..7c577a1 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -88,7 +88,7 @@ int __init pci_swiotlb_detect_4gb(void)
 {
 	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
 #ifdef CONFIG_X86_64
-	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
+	if (!no_iommu && max_possible_pfn > MAX_DMA32_PFN)
 		swiotlb = 1;
 #endif
 	return swiotlb;
diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
index c2aea63..a26bdbe 100644
--- a/arch/x86/mm/srat.c
+++ b/arch/x86/mm/srat.c
@@ -203,6 +203,9 @@ acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
 		pr_warn("SRAT: Failed to mark hotplug range [mem %#010Lx-%#010Lx] in memblock\n",
 			(unsigned long long)start, (unsigned long long)end - 1);
 
+	if (max_possible_pfn < PFN_UP(end - 1))
+		max_possible_pfn = PFN_UP(end - 1);
+
 	return 0;
 out_err_bad_srat:
 	bad_srat();
-- 
1.8.3.1