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

Closes: #908924

debian/changelog

@@ -267,6 +267,10 @@ linux (4.18.12-1) UNRELEASED; urgency=medium
   * [arm64] Update pinebook/teres-i device-tree patches to 4.19.x:
     - Enables the lid to wakeup from suspend.
 
+  [ Salvatore Bonaccorso ]
+  * [x86] swiotlb: Enable swiotlb for > 4GiG RAM on 32-bit kernels
+    (Closes: #908924)
+
  -- Ben Hutchings <ben@decadent.org.uk>  Mon, 08 Oct 2018 19:02:53 +0100
 
 linux (4.18.10-2) unstable; urgency=medium

debian/patches/bugfix/x86/x86-swiotlb-Enable-swiotlb-for-4GiG-RAM-on-32-bit-ke.patch

@@ -0,0 +1,50 @@
+From: Christoph Hellwig <hch@lst.de>
+Date: Sun, 14 Oct 2018 09:52:08 +0200
+Subject: x86/swiotlb: Enable swiotlb for > 4GiG RAM on 32-bit kernels
+Origin: https://git.kernel.org/linus/485734f3fc77c1eb77ffe138c027b9a4bf0178f3
+Bug-Debian: https://bugs.debian.org/908924
+Bug: https://bugzilla.kernel.org/show_bug.cgi?id=200709
+
+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@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>
+---
+ 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
+-- 
+2.19.1
+

debian/patches/series

@@ -100,6 +100,7 @@ bugfix/all/partially-revert-usb-kconfig-using-select-for-usb_co.patch
 bugfix/all/kbuild-include-addtree-remove-quotes-before-matching-path.patch
 debian/revert-objtool-fix-config_stack_validation-y-warning.patch
 bugfix/all/netfilter-ipvs-Fix-invalid-bytes-in-IP_VS_MH_TAB_IND.patch
+bugfix/x86/x86-swiotlb-Enable-swiotlb-for-4GiG-RAM-on-32-bit-ke.patch
 
 # Miscellaneous features
 features/all/kbuild-add-build-salt-to-the-kernel-and-modules.patch