[Xen-devel] [PATCH] [xen/swiotlb] Enable Xen-SWIOTLB only if running in privileged domain or if in non-privileged with iommu=soft.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

Previous to this patch we would unconditionally enable Xen-SWIOTLB
if running in PV context. That does not work with Xen 3.4.2 as it has a
security check to disable exchanging of MFNs if no PCI devices have been
passed through. In 4.0 there is an additional check to allow 2MB super-pages
- we accidentally circumvented that by exchanging pages under the 2MB chunk size
even without any PCI devices passed through.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/pci-swiotlb.c |    6 ++++--
 drivers/pci/xen-pcifront.c |    2 ++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/pci-swiotlb.c b/arch/x86/xen/pci-swiotlb.c
index ecdbfe2..6195eb9 100644
--- a/arch/x86/xen/pci-swiotlb.c
+++ b/arch/x86/xen/pci-swiotlb.c
@@ -960,7 +960,8 @@ xen_swiotlb_fixup(void *buf, size_t size, unsigned long 
nslabs)
                                dma_bits);
                } while (rc && dma_bits++ < max_dma_bits);
                if (rc)
-                       panic(KERN_ERR "xen_create_contiguous_region failed\n");
+                       panic(KERN_ERR "xen_create_contiguous_region failed: "
+                               "rc: %d\n", rc);
 
                i += slabs;
        } while(i < nslabs);
@@ -984,7 +985,8 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
 
 void __init xen_swiotlb_init(void)
 {
-       if (xen_domain()) {
+       /* For PV guest, only if iommu=soft is passed in. */
+       if (xen_pv_domain() && (xen_initial_domain() || swiotlb)) {
                printk(KERN_INFO "PCI-DMA: Using Xen software bounce buffering 
for IO (Xen-SWIOTLB)\n");
                xen_swiotlb_init_with_default_size(64 * (1<<20));       /* 
default to 64MB */
                dma_ops = &xen_swiotlb_dma_ops;
diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
index cc3b51b..3436202 100644
--- a/drivers/pci/xen-pcifront.c
+++ b/drivers/pci/xen-pcifront.c
@@ -1052,6 +1052,8 @@ static void __init_refok pcifront_backend_changed(struct 
xenbus_device *xdev,
        case XenbusStateInitWait:
        case XenbusStateInitialised:
        case XenbusStateClosed:
+               dev_warn(&xdev->dev, "Device is in %d state. Need to change "
+                       "state on the privileged domain.\n", be_state);
                break;
 
        case XenbusStateConnected:
-- 
1.6.2.5


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