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

[Eric Auger]

Hi Alex,

On 1/24/24 14:37, Alex Williamson wrote:
> On Wed, 24 Jan 2024 14:14:19 +0100
> Eric Auger <eric.auger@redhat.com> wrote:
>
>> Hi Alex,
>>
>> On 1/24/24 00:51, Alex Williamson wrote:
>>> On Tue, 23 Jan 2024 19:15:55 +0100
>>> Eric Auger <eric.auger@redhat.com> 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>
>>>> ---
>>>>  include/hw/virtio/virtio-iommu.h | 1 +
>>>>  hw/virtio/virtio-iommu.c         | 4 +++-
>>>>  2 files changed, 4 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..e7f299e0c6 100644
>>>> --- a/hw/virtio/virtio-iommu.c
>>>> +++ b/hw/virtio/virtio-iommu.c
>>>> @@ -1314,7 +1314,8 @@ 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;
>>>> +    s->config.input_range.end =
>>>> +        s->aw_bits == 64 ? UINT64_MAX : BIT_ULL(s->aw_bits) - 1;  
>>> What happens when someone sets aw_bits = 1?  There are a whole bunch of
>>> impractical values here ripe for annoying bug reports.  vtd_realize()
>>> returns an Error for any values other than 39 or 48.  We might pick an
>>> arbitrary lower bound (39?) or some other more creative solution here
>>> to avoid those silly issues in our future.  Thanks,  
>> You're right. I can check the input value. This needs to be dependent on
>> the machine though but this should be feasable.
>> Then I would allow 39 and 48 for q35 and 64 only on ARM.
> AFAIK AMD-Vi supports 64-bit address space.  Without querying the host
> there's no way to place an accurate limit below 64-bit.  Thanks,

Hum this means I would need to look at
/sys/class/iommu/<iommu>/amd-iommu/ or /sys/class/iommu/dmar* to
discriminate between AMD IOMMU and INTEL IOMMU physical IOMMU. Would
that be acceptable?

Eric
>
> Alex
>
>>>>      s->config.domain_range.end = UINT32_MAX;
>>>>      s->config.probe_size = VIOMMU_PROBE_SIZE;
>>>>  
>>>> @@ -1525,6 +1526,7 @@ 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(),
>>>>  };
>>>>