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 some Intel consumer processors, or when using a vIOMMU device with default settings.
The current error message is unclear, improve it and also change the error report to a warning because it is a non fatal condition for the VM. To prevent excessive log messages, restrict these recurring DMA mapping errors to a single warning at runtime. Reviewed-by: Alex Williamson <alex.william...@redhat.com> Link: https://lore.kernel.org/qemu-devel/20250206131438.1505542-6-...@redhat.com Signed-off-by: Cédric Le Goater <c...@redhat.com> --- hw/vfio/common.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/hw/vfio/common.c b/hw/vfio/common.c index 62af1216fc5a9089fc718c2afe3a405d9381db32..4fca4c6166f761acceb7b57b52e379603ea53876 100644 --- a/hw/vfio/common.c +++ b/hw/vfio/common.c @@ -555,6 +555,18 @@ static bool vfio_get_section_iova_range(VFIOContainerBase *bcontainer, return true; } +static void vfio_device_error_append(VFIODevice *vbasedev, Error **errp) +{ + /* + * MMIO region mapping failures are not fatal but in this case PCI + * peer-to-peer transactions are broken. + */ + if (vbasedev && vbasedev->type == VFIO_DEVICE_TYPE_PCI) { + error_append_hint(errp, "%s: PCI peer-to-peer transactions " + "on BARs are not supported.\n", vbasedev->name); + } +} + static void vfio_listener_region_add(MemoryListener *listener, MemoryRegionSection *section) { @@ -670,7 +682,10 @@ static void vfio_listener_region_add(MemoryListener *listener, strerror(-ret)); if (memory_region_is_ram_device(section->mr)) { /* Allow unexpected mappings not to be fatal for RAM devices */ - error_report_err(err); + VFIODevice *vbasedev = + vfio_get_vfio_device(memory_region_owner(section->mr)); + vfio_device_error_append(vbasedev, &err); + warn_report_err_once(err); return; } goto fail; -- 2.48.1
