When the IOMMU address space width is smaller than the physical
address width, a MMIO region of a device can fail to map because the
region is outside the supported IOVA ranges of the VM. In this case,
PCI peer-to-peer transactions on BARs are not supported.
This can occur with the 39-bit IOMMU address space width, as can be
the case on consumer processors or when using a vIOMMU device with
default settings.
The current error message is unclear. Change the error report to a
warning because it is a non fatal condition for the VM, clarify the
induced limitations for the user and provide advice on how to possibly
resolve this issue: setting the CPU address space width of the IOMMU
address space width accordingly.
Signed-off-by: Cédric Le Goater <c...@redhat.com>
---
hw/vfio/common.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index
3ca5dbf883ed2262e36952fcc47e717ff4154f12..561be7f57cf903e6e2bcbbb708be9e4d4ee8941c
100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -569,6 +569,20 @@ static bool vfio_get_section_iova_range(VFIOContainerBase
*bcontainer,
return true;
}
+static void vfio_container_p2p_error_append(VFIOContainerBase *bcontainer,
+ Error **errp)
+{
+ error_append_hint(errp, "PCI peer-to-peer transactions on BARs "
+ "are not supported. ");
+ if (vfio_viommu_preset(bcontainer)) {
+ error_append_hint(errp, "Try setting the vIOMMU \"aw-bits\" "
+ "property to match CPU address space width\n");
+ } else {
+ error_append_hint(errp, "Try setting the CPU \"phys-bits\" "
+ "property to match IOMMU address space width\n");
+ }
+}
+
static void vfio_listener_region_add(MemoryListener *listener,
MemoryRegionSection *section)
{
@@ -685,9 +699,13 @@ static void vfio_listener_region_add(MemoryListener
*listener,
"0x%"HWADDR_PRIx", %p) = %d (%s)",
bcontainer, iova, int128_get64(llsize), vaddr, ret,
strerror(-ret));
+ /*
+ * MMIO region mapping failures are not fatal but in this case
+ * PCI peer-to-peer transactions are broken.
+ */
if (memory_region_is_ram_device(section->mr)) {
- /* Allow unexpected mappings not to be fatal for RAM devices */
- error_report_err(err);
+ vfio_container_p2p_error_append(bcontainer, &err);
+ warn_report_err(err);
return;
}
goto fail;
--
2.48.1
