Re: [PATCH v2 1/3] virtio-iommu: Add an option to define the input range width

[Jean-Philippe Brucker]

Hi Eric,

On Thu, Feb 01, 2024 at 05:32:22PM +0100, Eric Auger wrote:
> aw-bits is a new option that allows to set the bit width of
> the input address range. This value will be used as a default for
> the device config input_range.end. By default it is set to 64 bits
> which is the current value.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> ---
> 
> v1 -> v2:
> - Check the aw-bits value is within [32,64]
> ---
>  include/hw/virtio/virtio-iommu.h | 1 +
>  hw/virtio/virtio-iommu.c         | 7 ++++++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/hw/virtio/virtio-iommu.h 
> b/include/hw/virtio/virtio-iommu.h
> index 781ebaea8f..5fbe4677c2 100644
> --- a/include/hw/virtio/virtio-iommu.h
> +++ b/include/hw/virtio/virtio-iommu.h
> @@ -66,6 +66,7 @@ struct VirtIOIOMMU {
>      bool boot_bypass;
>      Notifier machine_done;
>      bool granule_frozen;
> +    uint8_t aw_bits;
>  };
>  
>  #endif
> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
> index ec2ba11d1d..7870bdbeee 100644
> --- a/hw/virtio/virtio-iommu.c
> +++ b/hw/virtio/virtio-iommu.c
> @@ -1314,7 +1314,11 @@ static void virtio_iommu_device_realize(DeviceState 
> *dev, Error **errp)
>       */
>      s->config.bypass = s->boot_bypass;
>      s->config.page_size_mask = qemu_real_host_page_mask();
> -    s->config.input_range.end = UINT64_MAX;
> +    if (s->aw_bits < 32 || s->aw_bits > 64) {

I'm wondering if we should lower this to 16 bits, just to support all
possible host SMMU configurations (the smallest address space configurable
with T0SZ is 25-bit, or 16-bit with the STT extension).

Thanks,
Jean

> +        error_setg(errp, "aw-bits must be within [32,64]");
> +    }
> +    s->config.input_range.end =
> +        s->aw_bits == 64 ? UINT64_MAX : BIT_ULL(s->aw_bits) - 1;
>      s->config.domain_range.end = UINT32_MAX;
>      s->config.probe_size = VIOMMU_PROBE_SIZE;
>  
> @@ -1525,6 +1529,7 @@ static Property virtio_iommu_properties[] = {
>      DEFINE_PROP_LINK("primary-bus", VirtIOIOMMU, primary_bus,
>                       TYPE_PCI_BUS, PCIBus *),
>      DEFINE_PROP_BOOL("boot-bypass", VirtIOIOMMU, boot_bypass, true),
> +    DEFINE_PROP_UINT8("aw-bits", VirtIOIOMMU, aw_bits, 64),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> -- 
> 2.41.0
>