Re: [PATCH v2 8/9] vfio: Check compatibility of CPU and IOMMU address space width

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 30/1/25 14:43, Cédric Le Goater wrote:
> Print a warning if IOMMU address space width is smaller than the
> physical address width. In this case, PCI peer-to-peer transactions on
> BARs are not supported and failures of device MMIO regions are to be
> expected.
> 
> This can occur with the 39-bit IOMMU address space width as found on
> consumer grade processors or when using a vIOMMU device with default
> settings.
> 
> Signed-off-by: Cédric Le Goater <clg@redhat.com>
> ---
>   hw/vfio/common.c | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 5c9d8657d746ce30af5ae8f9122101e086a61ef5..e5ef93c589b2bed68f790608868ec3c7779d4cb8 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -44,6 +44,8 @@
>   #include "migration/qemu-file.h"
>   #include "system/tpm.h"
>   
> +#include "hw/core/cpu.h"
> +
>   VFIODeviceList vfio_device_list =
>       QLIST_HEAD_INITIALIZER(vfio_device_list);
>   static QLIST_HEAD(, VFIOAddressSpace) vfio_address_spaces =
> @@ -1546,12 +1548,28 @@ retry:
>       return info;
>   }
>   
> +static bool vfio_device_check_address_space(VFIODevice *vbasedev, Error **errp)
> +{
> +    uint32_t cpu_aw_bits = cpu_get_phys_bits(first_cpu);

This 'first_cpu' use is annoying. I understand the device is created
from the CLI, and passing the host physical bits limit as a device
property is not practical. We'll deal with that later...

> +    uint32_t iommu_aw_bits = vfio_device_get_aw_bits(vbasedev);
> +
> +    if (cpu_aw_bits && cpu_aw_bits > iommu_aw_bits) {
> +        error_setg(errp, "Host physical address space (%u) is larger than "
> +                   "the host IOMMU address space (%u).", cpu_aw_bits,
> +                   iommu_aw_bits);
> +        vfio_device_error_append(vbasedev, errp);
> +        return false;
> +    }
> +    return true;
> +}
> +
>   bool vfio_attach_device(char *name, VFIODevice *vbasedev,
>                           AddressSpace *as, Error **errp)
>   {
>       const VFIOIOMMUClass *ops =
>           VFIO_IOMMU_CLASS(object_class_by_name(TYPE_VFIO_IOMMU_LEGACY));
>       HostIOMMUDevice *hiod = NULL;
> +    Error *local_err = NULL;
>   
>       if (vbasedev->iommufd) {
>           ops = VFIO_IOMMU_CLASS(object_class_by_name(TYPE_VFIO_IOMMU_IOMMUFD));
> @@ -1571,6 +1589,9 @@ bool vfio_attach_device(char *name, VFIODevice *vbasedev,
>           return false;
>       }
>   
> +    if (!vfio_device_check_address_space(vbasedev, &local_err)) {
> +        warn_report_err(local_err);
> +    }
>       return true;
>   }
>