[PATCH 7/9] xen/swiotlb: With more than 4GB on 64-bit, disable thenative SWIOTLB.

[Konrad Rzeszutek Wilk]

If a PV guest is booted the native SWIOTLB should not be
turned on. It does not help us (we don't have any PCI devices)
and it eats 64MB of good memory. In the case of PV guests
with PCI devices we need the Xen-SWIOTLB one.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/pci-swiotlb-xen.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
index b6a5340..2f8cc57 100644
--- a/arch/x86/xen/pci-swiotlb-xen.c
+++ b/arch/x86/xen/pci-swiotlb-xen.c
@@ -8,6 +8,11 @@
 #include <xen/xen.h>
 #include <asm/iommu_table.h>
 
+#ifdef CONFIG_X86_64
+#include <asm/iommu.h>
+#include <asm/dma.h>
+#endif
+
 int xen_swiotlb __read_mostly;
 
 static struct dma_map_ops xen_swiotlb_dma_ops = {
@@ -49,6 +54,14 @@ int __init pci_xen_swiotlb_detect(void)
 	 * the 'swiotlb' flag is the only one turning it on. */
 	swiotlb = 0;
 
+#ifdef CONFIG_X86_64
+	/* pci_swiotlb_detect_4gb turns native SWIOTLB if no_iommu == 0
+ 	 * (so no iommu=X command line over-writes). So disable the native
+ 	 * SWIOTLB. */
+	if (max_pfn > MAX_DMA32_PFN)
+		no_iommu = 1;
+#endif
 	return xen_swiotlb;
 }
 
-- 
1.7.7.6


The next part is to deal with the user forgetting to pass in 'iommu=soft'
when doing PCI passthrough for a PV guest. This "forgetting" part is quite
annoying since it seems to happen to me all the time so I think that users
are more likely to forget it too.

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