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Subject[RFC PATCH 3/3] [RFC PATCH] iommu: allow fallback to swiotlb upon hw iommu initialization failure
When a hw iommu is detected during pci_iommu_alloc() it will disable
the swiotlb setup. If the subsequent hw iommu initialization in
pci_iommu_init() fails, the box may be left in an unusable state.

The swiotlb is normally allocated early from bootmem to ensure a large
(64M) contiguous allocation. This patch adds some logic to go ahead
and allocate the swiotlb despite the presence of a hw iommu, and later
free the swiotlb if it is not needed or enable it if it is. Because
pci_iommu_init() is called after bootmem has been released to the page
allocator, we use free_bootmem_late, a new mechanism for freeing pages
directly back to the allocator.

This patch relies on (iommu_detected && !dma_ops) being true as a way
to see the failed hw iommu initialization. This will not work w/ AMD
IOMMU in passthrough mode.

https://bugzilla.redhat.com/show_bug.cgi?id=524808

Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
arch/x86/include/asm/swiotlb.h | 4 ++++
arch/x86/kernel/pci-dma.c | 4 +++-
arch/x86/kernel/pci-swiotlb.c | 27 +++++++++++++++++++++------
include/linux/swiotlb.h | 3 +++
lib/swiotlb.c | 10 ++++++++++
5 files changed, 41 insertions(+), 7 deletions(-)
--- a/arch/x86/include/asm/swiotlb.h
+++ b/arch/x86/include/asm/swiotlb.h
@@ -9,9 +9,13 @@ extern int swiotlb_force;

#ifdef CONFIG_SWIOTLB
extern int swiotlb;
+extern void pci_swiotlb_alloc(void);
extern void pci_swiotlb_init(void);
#else
#define swiotlb 0
+static inline void pci_swiotlb_alloc(void)
+{
+}
static inline void pci_swiotlb_init(void)
{
}
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -141,7 +141,7 @@ void __init pci_iommu_alloc(void)

amd_iommu_detect();

- pci_swiotlb_init();
+ pci_swiotlb_alloc();
}

void *dma_generic_alloc_coherent(struct device *dev, size_t size,
@@ -300,6 +300,8 @@ static int __init pci_iommu_init(void)

gart_iommu_init();

+ pci_swiotlb_init();
+
no_iommu_init();
return 0;
}
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -42,18 +42,33 @@ static struct dma_map_ops swiotlb_dma_op
.dma_supported = NULL,
};

-void __init pci_swiotlb_init(void)
+static int swiotlb_try_init;
+
+void __init pci_swiotlb_alloc(void)
{
/* don't initialize swiotlb if iommu=off (no_iommu=1) */
#ifdef CONFIG_X86_64
- if ((!iommu_detected && !no_iommu && max_pfn > MAX_DMA32_PFN))
- swiotlb = 1;
+ if (!no_iommu && max_pfn > MAX_DMA32_PFN) {
+ if (!iommu_detected)
+ swiotlb = 1;
+ else
+ swiotlb_try_init = 1;
+ }
#endif
if (swiotlb_force)
swiotlb = 1;
- if (swiotlb) {
- printk(KERN_INFO "PCI-DMA: Using software bounce buffering for IO (SWIOTLB)\n");
+ if (swiotlb || swiotlb_try_init)
swiotlb_init();
+}
+
+void __init pci_swiotlb_init(void)
+{
+ if (!swiotlb && !swiotlb_try_init)
+ return;
+
+ if (iommu_detected && !dma_ops) {
+ pr_info("PCI-DMA: Using software bounce buffering for IO (SWIOTLB)\n");
dma_ops = &swiotlb_dma_ops;
- }
+ } else
+ swiotlb_free();
}
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -24,6 +24,9 @@ extern void
swiotlb_init(void);

extern void
+swiotlb_free(void);
+
+extern void
*swiotlb_alloc_coherent(struct device *hwdev, size_t size,
dma_addr_t *dma_handle, gfp_t flags);

--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -181,6 +181,16 @@ swiotlb_init_with_default_size(size_t de
}

void __init
+swiotlb_free(void)
+{
+
+ free_bootmem_late(__pa(io_tlb_overflow_buffer), io_tlb_overflow);
+ free_bootmem_late(__pa(io_tlb_orig_addr), io_tlb_nslabs * sizeof(phys_addr_t));
+ free_bootmem_late(__pa(io_tlb_list), io_tlb_nslabs * sizeof(int));
+ free_bootmem_late(__pa(io_tlb_start) , io_tlb_nslabs << IO_TLB_SHIFT);
+}
+
+void __init
swiotlb_init(void)
{
swiotlb_init_with_default_size(64 * (1<<20)); /* default to 64MB */


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