On Tue, Dec 22, 2009 at 11:19:19AM -0500, Konrad Rzeszutek Wilk wrote:
> On Tue, Dec 22, 2009 at 04:09:36PM +0000, Ian Campbell wrote:
> > On Tue, 2009-12-22 at 15:47 +0000, Konrad Rzeszutek Wilk wrote:
> > > > I thought it used to be that you could only (successfully) make order>0
> > > > increase_reservation or mem_exchange hypercalls if you had I/O
> > > > privileges? Has this changed?
> > >
> > > I am looking at the 3.4 code I am not seeing any I/O privileges check.
> > >
> > > I did not even know that those existed actually - could you give me an
> > > idea
> > > when was the last time you saw it?
> >
> > In xen-unstable multipage_allocation_permitted is called from
> > memory_exchange() and increase_reservation() and is defined as
> > #define multipage_allocation_permitted(d, order) \
> > (((order) <= 9) || /* allow 2MB superpages */ \
> > !rangeset_is_empty((d)->iomem_caps) || \
> > !rangeset_is_empty((d)->arch.ioport_caps))
> >
> > The ((order) <= 9) || is new and isn't present in the 3.4 tree,
> > previously you would have had to add a passthrough device to cause one
> > of the other rangesets to become non-empty.
>
> AAh, and since the exchange of memory is done in small chunks we pass
> underneath the radar even if did not have the passthrough device set.
>
> Ian, thanks for finding the culprit. Let me roll out a patch that
> will do what was done in the past (ie, turn SWIOTLB for DomU only
> when iommu=soft was passed in) as a fix.
Jeremy,
Please consider this patch to the PV-OPS tree.
[xen/swiotlb] Enable Xen-SWIOTLB only if running in privileged domain or if in
non-privileged with iommu=soft.
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>
diff --git a/arch/x86/xen/pci-swiotlb.c b/arch/x86/xen/pci-swiotlb.c
index ecdbfe2..7fdfccc 100644
--- a/arch/x86/xen/pci-swiotlb.c
+++ b/arch/x86/xen/pci-swiotlb.c
@@ -960,7 +960,7 @@ 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 +984,16 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
void __init xen_swiotlb_init(void)
{
- if (xen_domain()) {
+ int use_swiotlb = 0;
+
+ if (xen_initial_domain())
+ use_swiotlb = 1;
+
+ /* For PV guest, only if iommu=soft is passed in. */
+ if (xen_pv_domain() && !xen_initial_domain() && swiotlb)
+ use_swiotlb = 1;
+
+ if (use_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;
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