[tip:x86/urgent] x86/swiotlb: Enable swiotlb for > 4GiG RAM on 32-bit kernels

[tip-bot for Christoph Hellwig]

Commit-ID:  485734f3fc77c1eb77ffe138c027b9a4bf0178f3
Gitweb:     https://git.kernel.org/tip/485734f3fc77c1eb77ffe138c027b9a4bf0178f3
Author:     Christoph Hellwig <hch@xxxxxx>
AuthorDate: Sun, 14 Oct 2018 09:52:08 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 19 Oct 2018 07:49:32 +0200

x86/swiotlb: Enable swiotlb for > 4GiG RAM on 32-bit kernels

We already build the swiotlb code for 32-bit kernels with PAE support,
but the code to actually use swiotlb has only been enabled for 64-bit
kernels for an unknown reason.

Before Linux v4.18 we paper over this fact because the networking code,
the SCSI layer and some random block drivers implemented their own
bounce buffering scheme.

[ mingo: Changelog fixes. ]

Fixes: 21e07dba9fb1 ("scsi: reduce use of block bounce buffers")
Fixes: ab74cfebafa3 ("net: remove the PCI_DMA_BUS_IS_PHYS check in illegal_highdma")
Reported-by: Matthew Whitehead <tedheadster@xxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Matthew Whitehead <tedheadster@xxxxxxxxx>
Cc: konrad.wilk@xxxxxxxxxx
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20181014075208.2715-1-hch@xxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/pci-swiotlb.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index 661583662430..71c0b01d93b1 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -42,10 +42,8 @@ IOMMU_INIT_FINISH(pci_swiotlb_detect_override,
 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_possible_pfn > MAX_DMA32_PFN)
 		swiotlb = 1;
-#endif
 
 	/*
 	 * If SME is active then swiotlb will be set to 1 so that bounce