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 consumer processors or when using a vIOMMU device
with default settings. The current error message is unclear, also
change the error report to a warning because it is a non fatal
condition for the VM.
Signed-off-by: Cédric Le Goater <clg@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..5c9d8657d746ce30af5ae8f9122101e086a61ef5 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_once_err(err);
return;
}
goto fail;
--
2.48.1
On 30/1/25 14:43, Cédric Le Goater wrote:
> 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 consumer processors or when using a vIOMMU device
> with default settings. The current error message is unclear, also
> change the error report to a warning because it is a non fatal
> condition for the VM.
>
> Signed-off-by: Cédric Le Goater <clg@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..5c9d8657d746ce30af5ae8f9122101e086a61ef5 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);
Having vfio_get_vfio_device() returning NULL and
vfio_device_error_append() also checking for NULL is odd.
Maybe just inline everything here?
> + warn_report_once_err(err);
> return;
> }
> goto fail;
On 2/10/25 15:36, Philippe Mathieu-Daudé wrote:
> On 30/1/25 14:43, Cédric Le Goater wrote:
>> 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 consumer processors or when using a vIOMMU device
>> with default settings. The current error message is unclear, also
>> change the error report to a warning because it is a non fatal
>> condition for the VM.
>>
>> Signed-off-by: Cédric Le Goater <clg@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..5c9d8657d746ce30af5ae8f9122101e086a61ef5 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);
>
> Having vfio_get_vfio_device() returning NULL and
> vfio_device_error_append() also checking for NULL is odd.
Shouldn't vfio_device_error_append() check that its arguments are
safe to use ?
> Maybe just inline everything here?
I plan to use it elsewhere. See last patch.
Thanks,
C.
>
>> + warn_report_once_err(err);
>> return;
>> }
>> goto fail;
>
© 2016 - 2025 Red Hat, Inc.