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

Christoph Hellwig · Ingo Molnar · commit 485734f3fc77 · 2018-10-19T07:49:32.000+02:00
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: 21e07db ("scsi: reduce use of block bounce buffers") Fixes: ab74cfe ("net: remove the PCI_DMA_BUS_IS_PHYS check in illegal_highdma") Reported-by: Matthew Whitehead <tedheadster@gmail.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Matthew Whitehead <tedheadster@gmail.com> Cc: konrad.wilk@oracle.com Cc: iommu@lists.linux-foundation.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181014075208.2715-1-hch@lst.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git 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
