x86: Handle HW IOMMU initialization failure gracefully

If HW IOMMU initialization fails (Intel VT-d often does this,
typically due to BIOS bugs), we fall back to nommu. It doesn't
work for the majority since nowadays we have more than 4GB
memory so we must use swiotlb instead of nommu.

The problem is that it's too late to initialize swiotlb when HW
IOMMU initialization fails. We need to allocate swiotlb memory
earlier from bootmem allocator. Chris explained the issue in
detail:

  http://marc.info/?l=linux-kernel&m=125657444317079&w=2

The current x86 IOMMU initialization sequence is too complicated
and handling the above issue makes it more hacky.

This patch changes x86 IOMMU initialization sequence to handle
the above issue cleanly.

The new x86 IOMMU initialization sequence are:

1. we initialize the swiotlb (and setting swiotlb to 1) in the case
   of (max_pfn > MAX_DMA32_PFN && !no_iommu). dma_ops is set to
   swiotlb_dma_ops or nommu_dma_ops. if swiotlb usage is forced by
   the boot option, we finish here.

2. we call the detection functions of all the IOMMUs

3. the detection function sets x86_init.iommu.iommu_init to the
   IOMMU initialization function (so we can avoid calling the
   initialization functions of all the IOMMUs needlessly).

4. if the IOMMU initialization function doesn't need to swiotlb
   then sets swiotlb to zero (e.g. the initialization is
   sucessful).

5. if we find that swiotlb is set to zero, we free swiotlb
   resource.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: chrisw@sous-sol.org
Cc: dwmw2@infradead.org
Cc: joerg.roedel@amd.com
Cc: muli@il.ibm.com
LKML-Reference: <1257849980-22640-10-git-send-email-fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 13 insertions, 8 deletions

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index bed05e2e5890..a234e63c2656 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -124,24 +124,24 @@ static void __init dma32_free_bootmem(void)
 
 void __init pci_iommu_alloc(void)
 {
+        /* swiotlb is forced by the boot option */
+        int use_swiotlb = swiotlb;
 #ifdef CONFIG_X86_64
         /* free the range so iommu could get some range less than 4G */
         dma32_free_bootmem();
 #endif
+        pci_swiotlb_init();
+        if (use_swiotlb)
+                return;
 
-        /*
-         * The order of these functions is important for
-         * fall-back/fail-over reasons
-         */
         gart_iommu_hole_init();
 
         detect_calgary();
 
         detect_intel_iommu();
 
+        /* needs to be called after gart_iommu_hole_init */
         amd_iommu_detect();
-
-        pci_swiotlb_init();
 }
 
 void *dma_generic_alloc_coherent(struct device *dev, size_t size,
@@ -291,10 +291,15 @@ static int __init pci_iommu_init(void)
 #ifdef CONFIG_PCI
         dma_debug_add_bus(&pci_bus_type);
 #endif
-
         x86_init.iommu.iommu_init();
 
-        no_iommu_init();
+        if (swiotlb) {
+                printk(KERN_INFO "PCI-DMA: "
+                       "Using software bounce buffering for IO (SWIOTLB)\n");
+                swiotlb_print_info();
+        } else
+                swiotlb_free();
+
         return 0;
 }
 /* Must execute after PCI subsystem */